On iPhone 8 or later: quickly press and release Volume Up
On iPhone 8 or later: quickly press and release Volume Down
On iPhone 8 or later: press and hold the Side button until the Apple logo appears, then release
On iPhone 7 or 7 Plus: press and hold the Side button and Volume Down button together until the Apple logo appears, then release
On iPhone 6s or earlier: press and hold the Home button and the Side button together until the Apple logo appears, then release