how to recover old pasword for locked notes

More info is provided in link below , but as accurately stated in the 1st reply, there is no “recovery aid” available from Apple …

… other that the “hint” which could have been added when initially locking the note.

https://support.apple.com/en-au/guide/iphone/iphf177bb154/ios

It is not possible. If you lost the Notes password then nobody, including Apple, can open them.