Heater Knobs

Advice needed please . I need to remove the dashboard and assume the knobs need to be removed first [they are also I believe wrongly positioned ]. Working on they assumption they are held with a small slotted head screw  [out of sight and about 10 mm down the recess], I am having no joy in unscrewing them. Is there some trick to undoing them, or am I faced with drilling them out ?

Thanks, Terry

All the switch knobs are retained by an internal spring clip on the switch shaft. To release  you simply push the clip in with a suitable diameter rod or small screwdriver via the hole and pull the knob off the shaft. The heater control knobs may have been switched over by mistake previously.

Thanks Peter ,
Terry