Device Firmware Upgrade mode — DFU mode, for short — is a handy way of restoring an unresponsive iPhone back to its factory settings. Though rarely used thanks in large part of iOS's stability, the ability to boot up your iPhone into DFU mode is still an important knowledge to have in the event that your device becomes unstable or bricked.
Before we proceed, please note that restoring an iOS device via DFU mode will completely wipe it clean, so make sure to backup your iPhone X through iTunes or iCloud if you have important data that you can't live without. You have been warned! You can exit DFU mode fairly easily though, should you need to, if that scares you at all.
Mac or Windows computer
latest version of iTunes installed
Lightning USB cable
Step 1 Connect Your iPhone to Your Mac or PC
To get started, you'll need to connect your iPhone 8, iPhone 8 Plus, or iPhone X to your Mac or PC. Wait for your iPhone to fully connect, and launch iTunes if it didn't do so automatically since you want to make sure the program is able to fully sync with your iPhone.
Boot Your iPhone in DFU Mode
Before we get started, it is very important to note that if your iPhone either fully boots up or enters recovery mode by displaying "Connect to iTunes" on its screen at any point during this process, you'll have to go back to Step 1 to do it all over. As such, we highly recommend carefully reading through this step before physically attempting to do it in order to save time. That said, let's get started.
With your powered-up iPhone still connected to your computer with iTunes open, do the following steps.
1. Quick-press the volume up button.
2. Quick-press the volume down button.
3. Press and hold the side button until the screen goes black.
4. Release the side button once the screen blacks out, then ...
5. Quickly press and hold both the side and volume down buttons together for 5 seconds. After 5 seconds, release the side button without letting go of the volume down button. Continue holding down the volume down button for at least 5 seconds.
The key to that final step above is to pay close attention to your computer — if an iPhone recovery prompt from within iTunes pops up, release the volume down button and check your iPhone's display. If the screen is black, it means you've successfully entered DFU mode.
Now that you've successfully booted up your iPhone into DFU mode, you can hit "OK" to close the iTunes recovery prompt and proceed to restore it back to factory settings by selecting "Restore iPhone" under iPhone Recovery Mode inside iTunes. Once it's successfully restored, your iPhone 8, 8 Plus, or X will automatically exit out of DFU mode and boot up to its initial activation screen.