XR: Adding the ability to ascend/descend in the water with the right joystick

I am making a VR game with the VR template which comes ready with an XR origin. The origin has preset actions and corresponding scripts for basic locomotion (smooth move/turn, teleport, snap turn). I am trying to implement the ability to move up and down (ascend and descend) in a water environment, similar to the “EnableFly” ability, but instead of looking up with head relative forward source, the user uses their right joystick, pushing forward to dive, and pulling back to rise.
I’m lost as to how it all works. The left controller in the XR origin hierarchy for example, holds references to all of its input actions, which are sent to the Dynamic Move Provider? Which is a subclass of the Continuous Move Provider, which is not attached to any gameobject but actually applies the movement using the MoveRig() method?
How does Unity wants us to incorporate a new action for the user with the provided XR Origin. Any help is appreciated.
(Attached is the hierarchy of the XR origin with some unneeded objects disabled)