Sometimes, your iPhone or iPad isn't functioning correctly, and it enters in DFU mode, or Device Firmware Update mode. When this happens, you won't be able to use the device. It's screen will be black, and it won't be obvious whether it's working or not.
In this article, I'll explain how you can use iMazing to confirm that your iPhone or iPad is in DFU mode, how exit DFU mode, and how you can use iMazing to reinstall iOS on your device, if necessary.
Here's how to get your iPhone or iPad out of DFU mode:
Download and install iMazing on your Mac or PC computer
Download and install iMazing. Launch the app, and connect your device to your Mac or PC.
Launch iMazing. It will tell you if the device is in DFU mode.
Press and hold the Home and Power buttons on your device. For iPhone 7/7 Plus or higher: Hold down the Sleep/Wake + Volume Down key combination. After about ten seconds, the Apple logo should appear. If you don't see the Apple logo after few seconds, you will have to reinstall iOS: see this article.
You may need to reinstall iOS. To do so, see this article.