Apple has changed the method to force restart or hard reset an iPhone 8 or iPhone 8 Plus. Yet DFU and Recovery modes are same as iPhone 7 n 7 Plus. We gonna outline them in this here post.
While rebooting an iPhone 7 or iPhone 7 Plus requires pressing and holding both the Sleep/Wake and Volume Down buttons for at least 10 seconds, until the Apple logo appears, restarting an iPhone 8 or iPhone 8 Plus takes three steps.
Guide courtesy of MacRumors