https://support.apple.com/en-us/HT201263If you can't update or restore your iPhone, iPad, or iPod touch======================================================
https://support.apple.com/guide/ipad/restore-ipad-ipad9a74c804/iosRestore iPad
You can restore content and settings from a backup, or restore iPad to factory settings.
If you’re asked to enter your passcode and you’ve forgotten it, see Reset the passcode. If you’re asked to enter your Apple ID password and you’ve forgotten it, see the Recover your Apple ID website.
Erase then restore iPad from a backup
Important: You must first create a backup of your iPad. See Back up iPad using iCloud or iTunes.
- Go to Settings > General > Reset.
- Tap Erase All Content and Settings.
- Follow the setup assistant when iPad restarts.
The setup assistant gives you the option to restore iPad from an iCloud or iTunes backup. (See Turn on and set up iPad.)
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https://support.apple.com/en-us/HT204184Restore your iPhone, iPad, or iPod touch from a backup
Learn how to restore your device from a backup in iCloud or iTunes.