Calling LH with the booking code is probably easiest as taigatrommel already pointed out.
Now I don't know whether you are having a wanted stop-over in IAD, but if you don't and your ticket is flexible you might also wan't to look into the direct FRA-MCO flight. It's currently operated by an A330-300 with in-seat entertainment, so that might make the flight more bearable than in a B747 (assuming you are taking the LH operated flight from FRA to IAD).