Screen Time
how Can you change the passcode to your screen time but you don’t know the passcode?
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See this, If you forgot your Screen Time passcode - Apple Support This explains what to do if you forgot your Screen Time passcode. If you cannot reset it in that fashion, your only option is to restore the device to factory, set it up as new, and enter all your data manually. You cannot use a backup, as the Screen Time passcode is a part of the backup.