In each user account profile there is an 'Organization' tab with a 'Manager'
entry. If you go to the 'old' assistant's account you can go to that tab
and clear the 'Manager' box. Next, go to the 'new' assistant and go to that
tab and add the VP's name in the 'Manager' box.
I assume that the VP has a new assistant? I based my reply on this
assumption. You would change this on the 'assistant's user profile, not on
the VPs.