Press and quickly release the Volume Up button
Press and quickly release the Volume Down button
Press and hold the Side button
Keep holding until the Apple logo appears, then release
If the iPhone is frozen and will not respond, repeat the steps above
For iPhone 7 and iPhone 7 Plus, press and hold the Side button and Volume Down button together until the Apple logo appears
For iPhone 6s and earlier, press and hold the Home button and the Side button together until the Apple logo appears