If pressing the
BACK button
doesn't let you exit from an app, try the following:
- If your phone uses hardware navigation buttons, press and hold the BACK button and the POWER button at the same time.
Or if your phone uses onscreen navigation buttons, press and hold the BACK button and the RECENT APPS button 
at the same time.
-
If that works, it means you may have accidentally enabled screen pinning. Go to Settings, tap , and then tap the On/Off switch to turn screen pinning off.
