Shut the phone down like usual, then press and hold the power button till the recovery mode icon appears. Do not release at the Apple logo. When the recovery mode prompt appears, plug your iPhone into your Mac or PC. Open iTunes on your PC, or Finder on the Mac. Go to "iPhone", and click "Restore" on the popup.
Hope this helps!
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EDIT: This will wipe your data. Be careful with this!
For this you'll need:
* A Mac or PC (Windows 10 or 11)
* A USB to Lightning Cable
Shut the phone down like usual, then press and hold the power button till the recovery mode icon appears. Do not release at the Apple logo. When the recovery mode prompt appears, plug your iPhone into your Mac or PC. Open iTunes on your PC, or Finder on the Mac. Go to "iPhone", and click "Restore" on the popup.
Hope this helps!