As said by J Gregory, it is only a label. Same to turn a knob. It is not for up or down, but for right / left. Chose the command which will give the effect you are looking for. Does not matter its name.
LES/CMD/autopilot/APCP/turn_knob_pos
LES/CMD/autopilot/APCP/turn_knob_neg
The trim command description is for the "position" of the switch, not the trim itself. Probably not the best choice on our part, but for now it is what it is.
There were some changes added to X-Plane with regard to steering, which had not been adjusted for. This has been fixed for the next update and should resolve the steering issues.