Sometimes things can go wrong on your iDevice and the only way to solve them is by entering DFU mode, to do this simply follow the steps below:
1 Connect the device to a computer using a USB cable.
2 Quick-press the Volume Up button
3 Quick-press the Volume Down button
4 Hold down the Side button until the screen goes black, then hold down both the Side button and Volume Down button.
5 After 5 seconds, release the Side button while continuing to hold down the Volume Down button.
• If the Apple logo appears, the Side button was held down for too long.
6 Nothing will be displayed on the screen when the device is in DFU mode. If open, iTunes will alert you that a device was detected in recovery mode.
• If your device shows a screen telling you to connect the device to iTunes, retry these steps.
Click here to learn how to enter DFU mode on iPad, iPhone 6s and below, iPhone SE and iPod touch
Click here to learn how to enter DFU mode on iPhone 7&7plus