If the screen on your mobile device won't rotate, here's what to do.
iOS 12 or later: swipe down from the upper right corner of the screen,
less than iOS 12: swipe up from the bottom edge
Tap the lock symbol to turn off rotation lock.
For more info see the Apple Support page and
open Control Center
Android Device (like e.g. Samsung (Galaxy), Huawei, Sony and others
See : H E R E
Or search Google for the correct steps for your own device.