This article explains how to enable DFU mode (from English "Device Firmware Update") on iPhone and iPad. This is the most serious problem recovery mode available on an iOS device. When DFU mode is activated, the device will be restored via a computer, which will format the internal memory and reinstall all the necessary software, including the firmware whose function is to check all the hardware components of the device.
Steps
Step 1. Press and hold the top (or side, depending on your device model) button
It is located in the upper right part of the body or along the upper part of the right side.
Press and hold the indicated key until the device shutdown slider appears on the screen
Step 2. Slide the "slide to shutdown" slider to the right
The device will be turned off completely.
Step 3. Connect the iOS device to the computer
Use the cable that came with the iPhone or iPad. Connect the USB connector of the cable to a free port on your computer and the other end to the communication port on the device. In this case you will need to use the 30-pin or Lightning connector, depending on the iPhone model.
Step 4. Launch iTunes
It features an icon depicting a musical note.
iTunes may start automatically as soon as the device is detected
Step 5. Press and hold the top or side button on the iOS device again for 3-4 seconds
Step 6. Press and hold the Home button
Perform this step while still pressing the top or side button. The Home button has a circular shape and is located at the bottom of the front of the iPhone.
If you are using an iPhone 7 or iPhone 7 Plus, which does not have a physical Home button, you will need to press and hold the "Volume Down" key located along the left side of the iOS device
Step 7. Press and hold the two buttons indicated for 8-10 seconds
Do not release them until the Apple logo or a USB / Lightning connector icon appears on the screen
Step 8. Release the top or side button only when 8-10 seconds have elapsed
Step 9. Continue holding the Home button or the "Volume Down" key (on iPhone 7/7 Plus)
Perform this step until the notification message "iTunes has detected an [iOS device] in recovery mode" appears on the computer screen.
Step 10. Release the Home button or the "Volume Down" button (on iPhone 7/7 Plus)
The screen of the iOS device should appear completely black. You should now be able to restore it directly from iTunes.
