How to go about getting the Edge of a specific Surface of a Part?

So, I am trying to get the edge of one of the surface’s of part. I want to position my character from one surface edge, to the adjacent of another surface. In other words, let’s see I am moving my character along a part’s surface. When my character reaches the edge of that surface, I want it to place it on the edge of the adjacent surface to create sort of a transition.