Open Settings
Tap Control Center
Add Screen Recording to Included Controls if it is not already there
Open Control Center
On iPhone with Face ID, swipe down from the top-right corner
On iPhone with Home button, swipe up from the bottom edge
Tap the Screen Recording button
Wait for the 3-second countdown
To record audio, press and hold the Screen Recording button, then tap Microphone On
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