When you are in android studio 3 or above you need to add following lines AndroidManifest.xml file
<activity
android:name=".MainActivity"
android:configChanges="orientation"
android:screenOrientation= "sensorLandscape"
tools:ignore="LockedOrientationActivity">
One thing this is sensor Landscape, means it will work on both landscape sides
But if you only want to work the regular landscape side then, replace sensorLandscape to landscape