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. Hold down both the Home button and Lock button.
3. After 8 seconds, release the Lock button while continuing to hold down the Home button.
• If the Apple logo appears, the Lock button was held down for too long.
4. 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 iPhone 7&7plus
Click here to learn how to enter DFU mode on iPhone 8, 8+ and iPhone X