How to get my APC to return?

That can depend on where it is, but generally in the world map view you will see any APC's that are marching or out listed on the top left and tapping on their icon will take you to it and show you the options, if it is marching you may have a recall option (will require a recall item and the research unlocked though). If its camping or gathering there will be a return option.

If this doesn't help please reply with more details of what you are seeing.