Keychain - Forgotten Access Password

iMac 27" 5K running Catalina 10.15.1. Unable to remember Keychain access password which I am being asked for for a particular app. Is there a detailed cheat sheet with how to delete existing login in keychain and set up a new one?

I have had a message asking if I want to delete the all the associated login keychain files including referenced files but am not sure if I should select only some or all? Grateful for any advice.

Poppa46