force players in lobby to join server

I'm using the unity's lobby system and their Player class to tranfer data between the server and clients. I just don't understand how I can tell the other clients to do some things like switch scenes when the host of the lobby presses the start button. After pressing it the host should become the host using netcode and the other players should join his instance. I have no idea how to tell the other players to join the host after the host presses the button.

Doing it manualy works fine, when the other players click the "join" button to join the host, but I need to make it automatic. That's how lobbies work after all.

Can you help me get this running?

Any new thoughts on this?