iPhone 8 or later: Quickly press and release Volume Up
iPhone 8 or later: Quickly press and release Volume Down
iPhone 8 or later: Press and hold the Side button until the Apple logo appears
iPhone 7 or iPhone 7 Plus: Press and hold the Side button and Volume Down button at the same time
iPhone 7 or iPhone 7 Plus: Keep holding until the Apple logo appears
iPhone 6s or earlier: Press and hold the Home button and the Side or Top button at the same time
iPhone 6s or earlier: Keep holding until the Apple logo appears