Umpire incorrect foul call

[bwbuddy]

I was in C, working with a 1st year umpire. Partner rules a batted ball close to plate as a foul ball. Offensive coaches go ballistic and my partner comes out to talk to me. He says catcher picked it up while it was on the plate. So, I told him that would be a fair ball, but you've already called it foul. So, he says he understands, walks back to the plate, and all of a sudden reverses his call to fair. Of course, now the defense goes ballistic, thinking I had reversed the call. What would you have done at this point?