As the "SuperOwner" of a room you have the option to Ban & Un-Ban guests from your room. There are a couple of options that you can use to achieve this.

/Guestban will ban all guests from entering your room.

/Guestunban will remove the ban of all guests.

/Guestmircban will only ban guests using 3rd party clients to connect to chat as a guest.

/Guestmircban will only remove the ban of 3rd party clients chatting as guests.

This does not kick the current guest nicknames in the room. It only prevents them from joining.

The other option is to use the SuperOwner Room Access dialog which you can access using the room popup menu.

To add a guest ban you click the Add Access Button. Then in the entry box add >*