Notes Password Change

I'm sorry but you need to know the old password set on those notes; there is no way around it. You can set a new password on new notes but the old password is required for those notes that used it.

If you can remember the old password, then you'll be able to use a new password on those notes.

I understand your frustration but there is nothing we, or Apple can do. You are right: writing down your password or finding a foolproof way to remember it is the better solution at this time.

You are welcome to leave Apple a feedback about how you feel and how they could improve this: Product Feedback - Apple

That is kind of dumb if you think about it because I for example have a very important note locked and I can’t get into it because I forgot the password. The best thing to do is take the new password and write it down somewhere.