How to unlock my Notes password

See the following from How to lock notes on your iPhone, iPad, and iPod touch - Apple Support

If you forgot your notes password

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

If you have multiple passwords, you won't be able to tell which password you should use when you look at your Notes list. When you open a note locked by your old 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 enter the correct old password, you get the option to update that note's password to your current one.

Here's how to reset your Notes password: 

1. 1. Go to Settings > Notes, then tap Password.
   2. Select the Notes account that you want to change, then tap Reset Password.
   3. Enter your Apple ID password, then tap OK.
   4. Tap Reset Password again.
   5. Enter your new password and password hint. Tap Done.