Attempting to add an acting credit to an actor's page when the actor is already listed in the cast for that show.

I noticed while surfing IMDB that James Whitmore, Jr. is listed on the cast of two episodes of _The Rockford Files_, namely "Beamer's Last Case" and "Nice Guys Finish Dead". In both he plays the same character, Freddie Beamer. When I click on his name in the cast list, it properly links to his personal IMDB page with directing and acting credits; however, the two episodes of _The Rockford Files_ do not appear there.

I thought I could correct this by suggesting an edit to his IMDB page, and logged in and went to the editor, and entered the information. When I click on the button for review, however, the credit is rejected because "This person is already part of the cast. Rather than add them, please edit the existing credit". But there is no "existing credit" on Whitmore's page for _The Rockford Files_, so I don't know how to go about making this change. 

Can someone tell me how to update this? The credit on the page for _The Rockford Files_ appears to be correct, as far as it goes, I don't know how I would edit that to add it to Mr. Whitmore's personal IMDB page.