Hi @tanks23 -
Welcome to the forums!
QGC has been almost completely abandoned by Blue Robotics - a big docs update is coming soon! One of the driving reasons behind that was how hard it is to customize for applications like yours. Cockpit is much easier for this kind of thing!
With that said, you can find some information here - but generally it will depend on what version of ArduSub you’re using. Older versions only supported 3 additional output channels, while the latest stable lets you assign Actuator# to any pin #.