@Carrolb - when you access Yahoo mail via your browser, there is a gear icon in the upper right hand corner - place cursor on it for menu & select settings.
when you get settings select accounts you should get attached accounts - the one in question is the gmail - probably open the record by clicking the icon & reset/change the password being used when yahoo tries to access it.
It appears the password it has is no longer working. IF you want to combine the accts you need to fix it. If you do noit need to see both accts on the yahoo page, you can delete it.