How to close Facebook message notifications?

[Broomstick]

I don't want a particular message to keep notifying me, because it's a group chat and my friends keep chatting with each other. I don't want to leave the group because it's a leadership group, but them just talking about random stuff is really annoying cause I keep getting notifications. How do I turn off notifications for a particular message?
It's a facebook message notification, not the normal notification, there is no [x] button.