How to show a smaller second layout in Android keeping visible the main one?

Question

I am new in Android Studio where I am designing an app to control personal budgets. In the 'activity_second' there are two ExpandableListView that shows the data of the of incoming and expenses stored in several ArrayLists to the user. When the user press any of the ADD buttons I would like to open a smaller screen to input the new data, but at the same time maintain visible the content of the 'activity_second' in the background. I was researching but any solution I found satisfied this condition, how can I do it?

<androidx.constraintlayout.widget.ConstraintLayout 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="@drawable/background_color"
tools:context=".SecondActivity">
<ExpandableListView
    android:id="@+id/expandableIncomingsListView"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/button_incoming" />

<Button
    android:id="@+id/button_incoming"
    android:layout_width="60dp"
    android:layout_height="42dp"
    android:layout_marginTop="28dp"
    android:text="Add"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.079"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="@+id/text_incomings" />

<TextView
    android:id="@+id/text_incomings"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="28dp"
    android:text="@string/text_incomings"
    android:textColor="#ffffff"
    android:textSize="22dp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/text_expenses"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="28dp"
    android:layout_marginTop="200dp"
    android:text="@string/text_expenses"
    android:textColor="#ffffff"
    android:textSize="22dp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<ExpandableListView
    android:id="@+id/expandableExpensesListView"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/button_expense"
    app:layout_constraintVertical_bias="0.0" />

<Button
    android:id="@+id/button_expense"
    android:layout_width="62dp"
    android:layout_height="38dp"
    android:text="Add"
    app:layout_constraintStart_toStartOf="@+id/text_expenses"
    app:layout_constraintTop_toBottomOf="@+id/text_expenses" />

activity_second screenshot