Open the Settings app
Tap Control Center
Tap the plus sign next to Screen Recording if it is not already added
Swipe down from the top-right corner of the screen on iPhone X or later
Swipe up from the bottom of the screen on iPhone SE, iPhone 8, or earlier
Tap the Screen Recording button
Wait for the 3-second countdown
To stop recording, tap the red status bar or red clock at the top of the screen
Tap Stop
Find the recording in the Photos app