How to Reverse iPhone Update?

You generally cannot fully downgrade an iPhone to an older iOS version unless Apple is still signing that version

Check whether the older iOS version is still signed by Apple

Back up your iPhone before making any changes

Put the iPhone into Recovery Mode or DFU Mode

Use Finder on Mac or iTunes on Windows to restore the device

Download the signed IPSW file for the iOS version you want, if available

Restore the iPhone with the IPSW file through Finder or iTunes

If Apple is no longer signing the older version, you cannot officially reverse the update

Restore from an older backup only if it was made before the update

If you want to remove a beta update, unenroll from the beta program and restore to the latest public iOS version

Contact Apple Support if you need help with a restore or recovery issue