How to send alert or brodcast or Buzz to specific chatroom using RestAPI?

I want to send a message kind of alert or buzz to my specific room.
Let’s say, I am a member of the room and after 5 days I left the room and joined after 2 days I want to send an alert or buzz that I joined the room and have something to share an important message or else.
Is that possible ?
I used broadcast message API but it will trigger all other room too

The REST API plugin provides an administrative API for Openfire. It should not be used by clients at all!

I suggest that you implement this feature using XMPP instead: try sending a stanza that represents your desired functionality.