What should I do if I forgot my password in notes?

How to lock or unlock notes on your iPhone or iPad - Apple Support

Reset your notes password if you forgot it

To unlock a note, you need to enter the password that it's locked with. If you forgot your notes password, Apple can't help you regain access to your locked notes. You can create a new notes password or use your device passcode instead, but this won’t give you access to your old notes. If you set a new notes password or switch to your device passcode, you can protect any notes that you create going forward with the new password.

Click here and see the last section. This won't restore access to already-locked notes, but there isn't a limit to the number of times you can try guessing the old one.

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