How to Turn off Picture in Picture
First of all unlock your phone. And hold the app in front of the phone screen whose "picture-in-picture" you want to turn off
Touch and hold the app for a few seconds and click "App info" when it pops up
Click the "PIP" option to turn off the picture-in-picture function.
Now click on the button next to "Picture-in-Picture" This will turn off the picture-in-picture function.
For more information click on the button below