سلام وقت بخیر

مشکل شما در فایل xml ی که فرستادید این هست که layout_alignParentBottom رو به botton با ای دی btn_main_saveInformation اضافه نکردید.

android:layout_alignParentBottom="true"

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/gray100"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/tv_main_toolbarTitle"
        android:layout_width="match_parent"
        android:layout_height="56dp"
        android:background="@color/white"
        android:fontFamily="sans-serif-black"
        android:gravity="center_vertical"
        android:paddingStart="12dp"
        android:text="@string/app_name"
        android:textColor="@color/black"
        android:elevation="10dp"/>
    <Button
        android:id="@+id/btn_main_saveInformation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/background_primary"
        android:text="@string/saveInformation"
        android:textColor="@color/white"
        android:layout_alignParentBottom="true"
        />
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/btn_main_saveInformation"
        android:layout_below="@id/tv_main_toolbarTitle">
        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
            <CheckBox
                android:id="@+id/checkBox3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/uiDesign"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/checkBox2" />
            <Button
                android:id="@+id/button"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="12dp"
                android:layout_marginEnd="8dp"
                android:background="@drawable/background_primary"
                android:paddingStart="16dp"
                android:paddingEnd="16dp"
                android:text="@string/editProfile"
                android:textColor="@color/white"
                app:layout_constraintEnd_toStartOf="@+id/button2"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintHorizontal_chainStyle="packed"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/textView" />
            <TextView
                android:id="@+id/textView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="8dp"
                android:text="TextView"
                android:textColor="@android:color/black"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.498"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/imageView4"
                tools:text="motahareh" />
            <Button
                android:id="@+id/button2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="8dp"
                android:background="@drawable/background_botton_secondry"
                android:paddingStart="16dp"
                android:paddingEnd="16dp"
                android:text="@string/viewWebsite"
                android:textColor="@color/gray600"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.5"
                app:layout_constraintStart_toEndOf="@+id/button"
                app:layout_constraintTop_toTopOf="@+id/button" />
            <androidx.constraintlayout.widget.Guideline
                android:id="@+id/guideline2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_constraintGuide_begin="24dp" />
            <TextView
                android:id="@+id/textView2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="32dp"
                android:text="@string/skills"
                android:textColor="@color/gray600"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/button" />
            <TextView
                android:id="@+id/textView3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="12dp"
                android:text="@string/provinceCity"
                android:textColor="@color/gray600"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/checkBox3" />
            <RadioGroup
                android:layout_width="135dp"
                android:layout_height="101dp"
                android:layout_marginTop="8dp"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/textView3">
                <RadioButton
                    android:id="@+id/radioButton"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/alborzKaraj" />
                <RadioButton
                    android:id="@+id/radioButton2"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/gilanRasht" />
                <RadioButton
                    android:id="@+id/radioButton3"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/tehran" />
            </RadioGroup>
            <CheckBox
                android:id="@+id/checkBox"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="8dp"
                android:text="@string/androidDevelopment"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/textView2" />
            <CheckBox
                android:id="@+id/checkBox2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/deepLearning"
                app:layout_constraintStart_toStartOf="@+id/guideline2"
                app:layout_constraintTop_toBottomOf="@+id/checkBox" />
            <ImageView
                android:id="@+id/imageView4"
                android:layout_width="80dp"
                android:layout_height="80dp"
                android:layout_marginTop="24dp"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintHorizontal_bias="0.498"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:srcCompat="@drawable/taheri" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </ScrollView>
</RelativeLayout>