If you forgot your new iPhone passcode, you can reset it with your old one up to three days later. This can save you hours of trying to remember the new passcode, or worse, resetting your phone from a backup.
You just have to tap Forgot Passcode? on the Lock Screen after you enter it several incorrect times.
Keep reading for a detailed walkthrough. And don’t worry — if you change your passcode intentionally to keep someone out, you can instantly expire your old one.