There is no rule when to use which one, particularly in circumstance of um. You need to simply study which verb calls for a single of those a few terms. Some verbs and phrases use um and there's no motive why: du wirst gesucht haben ihr werdet gesucht haben du https://tysonelrxc.wikiparticularization.com/814468/new_step_by_step_map_for_gesucht