Under Select Joystick, move your rotary that you want the trim to, notice which numbers change, select the input on the right and what you want it to do on the left. Click "Set Input." Calibrate the joystick; the rotaries count as an axis and need to be moved and centered.
I've posted on this three times, and every time someone has some massively complicated, overdone way of doing it.
If this doesn't work, I'm guessing that the axis is dead.