If you enter the correct old password, you get the option to update that note's password to your current one. When you open a note locked by an old notes password but you enter your current password, you'll see an alert that you entered the wrong password with a hint for your old password. If you have multiple notes passwords, you won't be able to tell which password you should use when you look at your Notes list. 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. 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 forgot your notes password, Apple can't help you regain access to your locked notes. To unlock a note, you need to enter the password that it's locked with. Reset your notes password if you forgot it Use Face ID or Touch ID, or enter your previous notes password. Select the Notes account that you want to change, then tap Change Password. If you choose to use your device passcode to lock notes but later remove your passcode from the device, you can still access the notes you locked with your passcode.
