I need help with xbox controls

Ok so in every rts game i play, control groups are available, aswell as adding units and removing units after "selecting all units" in order to split your army or to leave specific units behind. I for the life of me cannot figure out how to do this for dune on xbox. I know its there because I've seen it done on pc. On xbox I can either select all units, or select only all units of one type... i cant, for example, select all my melee fighters and detenators, but leave behind my freelancers and planes; unless i literally move every unit i want 1 by 1 to an offscreen area and then select all in new area. Super tedious, plz help.