heater flap 2000 Jimmy

No air flow to floor. Switching air flow to panel and defrost without problem. Acts like flap that diverts air to floor not moving.
The vacuum motor is moving(left side near gas pedal)
Suggestions?
Also how do I get to heater flap in box? What do I have to take apart to get into it?

Thanks

I dont remember if i saw the flap but in my 2000 jimmy if you open the glove box and then on the top left push up the metal spring tab the glove box will swing down and you can see the heater box.