I have a lock on Notes. I can't remember my password. How do I reset it?

That is not possible. You will need to keep trying until you remember the password that you chose when you created that note.

See How to lock or unlock notes on your iPhone or iPad - Apple Support

Particularly this portion:

To unlock a note, you need to enter the password that it's locked with. If you forgot your notes password, Apple can't help you regain access to your locked notes. You can create a new notes password or use your device passcode instead, but this won’t give you access to your old notes.