How do I enable generation from a mod?

Hello! I got interested in the TerraFirmaCraft mod and would like to play with my friends. But to be able to play with this mod, you need its own generation of the world, but I can't create it. How do I enable world generation from the TerraFirmaCraft mod?

Yes, this mod has its own world generation. When I create a single player game it is there.