Then you have just learned how incredibly important that locked notes password was to remember. You can try forever, but until you remember the locked notes password, the notes will remain locked. If you can't remember it, they will remain locked forever.
When you created the locked notes password, you were given the opportunity to create a password hint. If you didn't, that's going to make it harder to recall the password.
It is critically important to note important passwords somewhere for future recall. Something as simple as a little notebook kept in a safe location, can be a good place to write important passwords down.
There is nothing anyone here or at Apple can do to help you in this regard.