Sterling Cooktop?

I have a Sterling Cooktop that is over 20 years old. Model #is GCT361/5D. My problem is the ventilator fan is in the up position and will not go down. I had an appliance repair company come out to work on the switch but they cannot figure out how to remove the glass top to get to the switches. I have tried a couple of things but cannot figure it out either. Does anybody know how to remove the top so you can get at the switch mechanisims?