Let me explane better; due a wrong aircraft recognize (I suppose) GSX read a freight aircraft like a passenger aircraft; this mean that the main upper cargo door don't have a cargo loader but a stair.
A cargo door will never have a stair, unless your configuration is so wrong, that you moved a passenger door in a cargo door location.
The current airplane configuration editor has a parameter where you can tell GSX if an airplane is a cargo or not, but this will effect ONLY the passenger boarding sounds, that will not play if it's a cargo plane, but you will still have to set all doors correctly, and eventually remove passenger doors not used.
To have the cargo pallet loading in the correct direction, you must move on the left side of the plane what by default is the FRONT cargo loader.