To hack each of the three servo’s start by removing stickers and the small band of shrink tubing holding it together. Remove the top part and remove all of the gears, including the pinion (if your propellers do not match the motor shaft, you can alternatively keep on the pinion and drill out the propeller to fit that). Remove the bottom part and carefully pull out the motor and pot. The motor most often comes out easy, the pot is glued in. Most often you can still pull it out by moderately pulling on the wires. I you feel unsure you can alternatively break open what is left of the servo casing, with small pliers.
Protect the circuit board from accidental short circuiting by wrapping a single layer of tape around it.
Test by connecting to the receiver with the propellers left off. Power up and trim each pot till the motor doesn’t move with the transmitter’s corresponding stick at neutral position.
Choose which motor/function you want on what stick. I usually put the up/down on what is normally the “throttle” (because a stick without auto centering is convenient here), the main propulsion on the “elevator” and the left/right on the “ailerons” (on a mode 2 transmitter).