OK, the throttle is on the base infront of the stick, right?
First be sure its registering in windows, so go to game controllers in Control panel and calibrate etc.
Then (this is where it gets tricky) -- new setup system in AH only a month or so old, so this is from memory...
Controls/map controllers/mode 1
select your controller
The throttle will likely register as one fo the "axis" options. You can tell which by sliding the throttle up and down -- you shoudl see the digital readouts next to the axis pop up and down too.
Select that axis, click modify, select the throttle1 input, and you should be there.