How to do that? I wanted to have some different opponents than the preinstalled ones, but I couldn't find out how to do it. I connected to the G2G account here, but I have no idea. Is there a documentation somewhere?

I think I got it, I'll first have to add them here to my collection and then I can select in the game from those that I picked here. I'll try that. I thought I could browse them from within the game.