Channel Assingment

I am new to this field and I am trying to build some kind of little robot
I have 2 motors I use for driving and a 3th motors that i want to connect in order to more flippers that will be used in case the robot needs to flip it selfe

My problem is that I dont know how to assign the Servo output to the RC commands (I have connected the motor conntroller to Servo Output 6) and I dont even see all of the joysticks on the Mission planner (I have 5 and the Mission planner shows only 4)

Does anyone knows how I can do it?

I am using
Herelink controller + antenas
Arupilot PX4 with the hex cube (black)

Thank you very much anyway :smiley: