Open Quick Settings by swiping down from the top of the screen
Tap Auto-rotate, Portrait, or Screen rotation to enable rotation
Open the app or screen you want to rotate
Turn the phone sideways to switch to landscape mode
If rotation does not work, check Settings
Go to Settings
Tap Display
Tap Auto-rotate screen or Screen rotation
Turn the toggle on
If needed, restart the phone
If a specific app does not rotate, check whether the app supports rotation