Restore iPhone using iTunes is to purge the memory of your smartphone and upgrade to the latest version of iOS through this app.
Here's how to perform an iPhone restore through iTunes:
Step 1: Download the latest version of iTunes
> Plug iPhone via cable to connect your computer.
Note: Turn off your iCloud account's phone search function before proceeding. (Settings >> iCloud >> Find iPhone off).
Step 2: Back Up.
Step 3: Restore and update.
Step 4: Next.
Step 5: Agree.
Step 6: Wait for update.
Step 7: Done.
Step 8: Wait for update and restore settings.
Then restore the iPhone via iTunes will be successful.
In addition, beside iTunes, you can also refer to two third-party iPhone management tool such as 3uTools. Good luck!