Open Settings
Tap Control Center
Tap the Add button next to Screen Recording if it is not already included
Swipe down from the top-right corner of the screen on iPhone with Face ID
Swipe up from the bottom edge of the screen on iPhone with a Home button
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
Tap Stop when prompted
Find the recording in the Photos app