How to Setup a Skid Steering on Mission Planner and Herelink by only using one joystick?

Hello, I’m trying to setup a skid steering rover and my transmitter is herelink.

Suppose I only want to use one joystick for the rover’s skid steering (throttle left and throttle right). How can I configure this one?

These are the parameters that I have set in Mission Planner.
Servo1_Function: 73
Servo3_Function: 74

Are there any configuration that I missed aside from these? Thanks