Back up your iPhone if needed
Turn off your iPhone
Press and release the Volume Up button
Press and release the Volume Down button
Press and hold the Side button until the Apple logo appears
If you want a full factory reset, go to Settings
Tap General
Tap Transfer or Reset iPhone
Tap Erase All Content and Settings
Enter your passcode
Confirm the reset
Wait for the iPhone to erase and restart
Set up the iPhone as new or restore from a backup