The note if forever locked with the password used. There is no way to reset it. You can change your password used, but that will only affect new notes that you lock. This is all detailed in the Apple Support article dealing with locked notes here: How to lock or unlock notes on your iPhone or iPad - Apple Support
The relevant portions are:
If you use a unique password for Notes, there is no way to access your locked notes if you forget the password. If you forget this password, you can reset your notes password and use your new password to lock other notes. If you access your iCloud notes on more than one Apple device, use the same notes password to lock and unlock all of them.
Apple doesn't have access to locked notes and can’t help you access them if you forget your notes password. If you forget your notes password, resetting the password doesn’t give you access to previously locked notes. If you reset then create a new notes password, that only allows you to lock other notes.