Thank you ZoltanJr but this is not what i look ,
because i want a client move to another map not all client in te same time 
exi say : An MMO is not done with one Server. An MMO has one Server per Map Instance. The Maps in UE4 can be pretty big, but yes, you can not have more than 1 map per Server, so you need a system that creates servers and removes them and moves players between them, so you can have multiple players in it.
Also i doubt that the UE4s networking system can handle the playercount of an MMO, so you might want to create your own Server System for that.
system that creates servers and removes them and moves players between them
it is possible to do it in blueprint?