I'll be giving you three methods you can use when faced with such a difficulty. The options available on this post are
#1:Doing a DFU Restoration
#2:Performing hard reset
#3:Restoring the device through iTunes.this alternative won't be seriously dealt with because it's actually a step in performing DFU restore.
Option 1:How To Unbrick iOS Devices By Performing DFU Restoration
If you receive an error while performing hard reset which is the first method above of restoring device via iTunes, you should do a DFU restore. This means, you have to completely wipe the phone and reset the device to the original factory state where all your input will be deleted.
•Firstly, plug the iPhone to a PC and launch iTunes.
•Then, press and hold the volume key for some seconds.
•After that, release the power key and hold on to the home button until you receive a message saying "iTunes has detected an iPhone in recovery mode.".
•Now free the home button and your device will go black. If it does not, kindly restart the process.
Option2:How To Unbrick iOS Devices By Performing Hard Reset
•It's simple and easy. Just hold the power button and the home button and wait for the iPhone to reboot.
•Then, you will see the Apple logo and it will automatically boot to iOS or ask you to plug into iTunes. After that, your phone has successfully entered recovery mode. Kindly connect to PC and open iTunes.
•After connecting your phone to your PC and has successfully launched iTunes, the next step is to click on RESTORE from the right-hand menu.
•Kindly CONFIRM any pop-up that follows and wait till the restoration is complete.
If your phone doesn't seem to respond or it still misbehaves after carrying out any of the options, I suggest you take your phone to an official iOS centre for repair.
Hope this article was helpful. If you have any contribution or comment,kindly use the Comment Box

