I think you should connect the Storm to a serial port of your flight controller and then use the serial or Mavlink protocol to move the gimbal. You have to use the angle option, I think (did not work with these boards for some time, but they are great, especially the NT protocol!).
Maybe there is an option to switch between pitch and yaw by toggeling another channel. But I do not know, you have to look for that (probably by using scripting?). If not you will have to use two HereLink buttons and configure them as multi buttons..
http://www.olliw.eu/storm32bgc-wiki/Using_STorM32_with_ArduPilot
https://ardupilot.org/copter/docs/common-storm32-gimbal.html?highlight=storm32