As far as I know, they have a single RGB and fan header and with the 3-pack they have the connections for the hub directly because otherwise you would have far too many individual RGB and fan headers. But you can also simply use the connection of the 3-pack for the single fan. Otherwise, if you don't have one, you have to plug the fan into the mainboard separately.

If you have not bought a 3-pack beforehand, you will have to connect it to the mainboard, as the adapter cable to the hub is not included with the single. All alternatives are currently not available. There would be the Uni hub Sl-inf, Controller Lian-Li UNI HUB SL-INF Controller, L-Connect 3 (16 x)
But this is not available.