AUX1 and AUX2

I am wondering how I can potentially link aux1 and aux2 values to something on a handheld joystick.

I am using a modified version of the PX4 firmware for an omnidirectional vehicle, and I believe that different degrees of freedom will be controlled with two sticks depending on what the aux values are at. There are if statements in the code based on the aux values that change the roll/pitch angles, so I am curious how I can change those aux values to allow for this wider control in real time.