Changing a gamemode mid game

Hello, i have a problem.
I have a map, for the main menu and for the actual game.
In the main menu, i have my own gamemode, and as for the actual game, i have the thirdpersongamemode.
How can I change the gamemode on open level?

The thing it does right now is, that it opens the level, but i won’t move with the actual character.