To change layout go to your xml code and change your root layout to desired layout, if it shows error, post error message here.

This part is from my other answer:
https://stackoverflow.com/a/42779569/3870382
To change defalut layout when creating an Activity, you can modify default template layout file in Android Studio resources, go to your Android Studio folder and go to following folders path to it:
\plugins\android\lib\templates\activities\common\root\res\layout
Edit file simple.xml.ftl and change layout to your choice, notice that some layouts require additional elements (e. g. LinearLayout needs android:orientation), save file and create activity in Android Studio, you should get an Activity with xml layout that you changed.
Mine looks like this (I had 2.2.3 in that time so I have still RelativeLayout)
(You should see your constrainLayout in this file, so change it to relativeLayout)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
<#if hasAppBar && appBarLayoutName??>
xmlns:app="http://schemas.android.com/apk/res-auto"
</#if>
android:id="@+id/${simpleLayoutName}"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
<#if hasAppBar && appBarLayoutName??>
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/${appBarLayoutName}"
</#if>
tools:context="${relativePackage}.${activityClass}">
<#if isNewProject!false>
<TextView
<#if includeCppSupport!false>
android:id="@+id/sample_text"
</#if>
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!" />
</#if>
</RelativeLayout>