It is further up to the right looking at your picture. If I remember correctly, you need a mirror to see it, but there is enough room to get your hands in there and with a small enough bit, you can get the screws out.
The blend door is moved by the temperature actuator.
This schematic will illustrate which door performs each function:
So as you can see, you could either have a problem with a broken blend door, or an improperly calibrated or defective actuator. You could run through the recalibration procedure... I cannot look it up for you right now, but I know it has been posted before.