the command is servertravel /Game/directory to the map file/mapname. For my game the maps are all located in the folder Maps under the Content root in the Editor. Therefore the command for me is servertravel /game/maps/lobby. At the end I declared ?listen to tell the server to maintain an open internet connection. All players that are already connected to the server will travel even without ?listen but, and I may be mistaken on this last part, if you remove ?listen the server will close its door so new players can not join until you create a new session.
Furthermore I do not know if this is required but I saw this command run in the Game Mode in every tutorial I watched. It could be the only place that server travel is possible…I’m not sure.