how do i work the heater in my 1973 beetle

What heater? It's an air cooled engine and heat comes through tunnels from the exhaust headers.

check all air ducts, for leaks, make sure rear fan is spinning, then ck. deverter cables and duct flaps on heat tubes

Their is none it comes from the tunnels provided by the engine

If your car is quipped with the auxiliary heater ,just pull the knob for it-to the left of the stick shift diagram on the lower part of the instrument panel.The light should turn green.The engine should be running to save the battery or only run it for a short time say 25 to 30 min.Or the control might be over the radio.I have seen this in the owner's manual of a '71 '73 control might be different.