If you have an iPhone 8 or later: press and release the Volume Up button, press and release the Volume Down button, press and hold the Side button until you see the Recovery Mode screen

For an iPhone 7 or 7 Plus: Press and hold the Side button and Volume Down button until you see the Recovery Mode screen.

On iPhone 6s or earlier: Press and hold both the Power button and the Home button until you see the Recovery Mode screen.