A phone call should be able to effectuate what you are proposing, but to answer the question, in the morning the UA counters at MUC will have a handful of "real" UA agents available, along with contractors. Usually these agents can be found at the GS/1K/Polaris counter or across the room at the actual United ticket office. Out of MUC, I am usually on the EWR flight (UA31, 0930) so this is generally earlier in the morning, like 0745 or so.