Before you get to the steps, turn off Find My on your iPhone or iPad by going to Settings > your name from the top > Find My > Find My iPhone/iPad. Once Find My is off, you can restore the device using your Mac or PC.

1. Plug your iPhone or iPad into your computer using an appropriate cable. If a message appears asking for a passcode or to Trust this Computer, follow the prompts and allow that.
2. Open Finder on Mac or Apple Devices app/iTunes on your Windows PC.
3. Locate your iPhone or iPad. In Finder, it simply means clicking the iOS device name in the left sidebar.
4. Click Restore iPhone from the General or Summary section.
5. A message may appear asking if you first want to back up your device. If you do, select Back Up. If not, select Don’t Back Up. Of course, you can also back it up even if you don’t get a popup.
6. You’ll then see a final warning that says something like: Are you sure you want to restore the iPhone to its factory settings? All of your media and other data will be erased. If you’re sure, click Restore to erase your phone and bring it to factory settings.