My recall is that is a large rubber plug with a hole in the middle for the wires to go through the fire wall. On the engine side there is a large glob of black body putty to stop and water or air from passing through to the passenger compartment. I just pushed the rubber plug from the inside to pop it out of the hole. Then removed all the old body putty off the rubber plug (cleaned up with mineral spirits), put the rubber plug back into the hole and resealed with 3M black body putty strips.
Pic attached, front and back
