Separating a private starboard from a public one

Currently trying to set up a starboard for a private chat as we have ran out of pins, and I can't seem to figure out how to get it to work. I would like the messages from "morbius-club" and "morb-2" to be the only ones that can reach this starboard, and then I will have a separate starboard for messages in every other channel, but it doesn't work when I hit the star. Thanks