Where should I go old notes password

You can't retrieve it unless you kept a copy yourself, but there isn't a limit to the number of times you can try guessing it.

Resetting the password won't restore access to already-existing notes.

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If you locked notes, the locked notes password is encrypted, meaning there is nowhere you can go to get the password. You have as many tries as you want to remember the password, but until you remember it, the notes will remain locked, possibly forever, unless you can remember the password.

You were given the opportunity to create a locked notes password hint at the time you locked the notes. Did you? And important passwords such as these should be written down somewhere for future recall to avoid situations like this.

Apple can't help you find the password. No one can. Only you can unlock the notes with the correct password.