How can I reset forgotten password in notes?

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

“If you forgot your notes password

To unlock a note, you need to enter the password that it's locked with. If you forgot the password, Apple can't help you regain access to your locked notes. You can create a new password, but this won’t give you access to your old notes. A new password will let you password protect any notes that you create going forward with the new password.”

You can't. There is no way to reset a a password used to lock a note. If you can't remember it, you can't open it. Passwords such as this, which are very important should be written down somewhere for situations like this. Sorry.

Sorry, although you can reset the password, you can't for secured notes and there will be no way to recover them without knowing the password used to secure them.