I found this video in a quick search, it shows how you need to select Joystick (HID) instead of USB Storage, however it is in russian:
https://www.youtube.com/watch?v=-G0EAMnf5aQ
You may also need to switch Internal RF mode off. Not sure if this applies , but at least on older style Taranis' - If you are flashing your Taranis with new firmware, make sure you deselect the "mass storage" option, otherwise joystick emulation is disabled.