how do I go about configuring those for pushback to work properly?ir do I have to do nothing and gsx automatically reads these changes?
GSX reads the AFCAD automatically, any change you do to the AFCAD is always detected. Usually, you'll want to edit the scenery AFCAD only when there are obvious errors, like missing links, overlapped nodes, orphaned parkings, because these will likely result in GSX failing to work.
Other things that are not strictly "errors", are easier to fix in the GSX parking configuration editor, for example the Pushback preference (which many developers forget to set, because ADE defaults to "none"), or the parking radius, or the presence of a fake/static jetway that GSX can't detect.