If your screen is black or has frozen
If your screen is black or has frozen, you may need to force-restart your device. A force-restart won't erase the content on your device. You can force-restart your device even if the screen is black or the buttons aren't responding. Follow these steps:
iPad models that don't have a Home button: press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Power button until the device restarts.
iPhone 8 or later: press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Side button until you see the Apple logo.
iPhone 7, iPhone 7 Plus and iPod touch (7th generation): press and hold both the Top (or Side) button and the Volume Down buttons until you see the Apple logo.
iPad with Home button, iPhone 6s or earlier and iPod touch (6th generation) or earlier: press and hold both the Home and the Top (or Side) buttons until you see the Apple logo.