I forgot the password for my locked notes. How can I reset the password?

You cannot. You can set a new password for new notes. But there is no way to reset an existing notes password.

See -> How to lock or unlock notes on your iPhone, iPad, and iPod touch - Apple Support

“Don't forget your Notes password. Apple doesn't have access to locked notes and can’t help you access them if you forget your password. If you forget your Notes password, resetting the password doesn’t give you access to previously locked notes. Resetting then creating a new Notes password only allows you to lock other notes.”