Changing Calendar Users/Viewers

I am currently serving as the stake executive secretary. Last year I set up a private stake presidency calendar and designated, by position, who is able to view and edit this calendar. I want to add one additional viewer/editor but the system does not allow me to do this. When I access this calendar through Calendar Settings, the stake executive secretary's permission is view and edit but this calendar title reads Stake Presidency (private) (View Only).

Any suggestions?

Thank you.