Forgot passcode to open locked note

Then you will not be able to open that note, sorry.

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.”