You can't, they modeled only 1 cargo door, 1 passenger door and 1 catering door to be animated, the other are static. That is because the default Ground service vehicles don't work in pairs, so they modeled only the doors usable with the default services.
If an airplane hasn't modeled a door to be animated and linked to a variable, there's nothing GSX can do about it, but we intentionally set the default configuration for the default airplanes to have all door configured, so users would see GSX can have pairs of services working together but, of course, since the door in those airplanes are static, you'll see crew or passengers passing through a closed door. If you don't like that, you can just Disable the door ( set it to "no door" ) in the airplane configuration editor, so no service will be performed there.
