Engage is built around the concept of patient rooms. If joined a patient room, you'll receive a notification any time someone in the room sends a message. Even if you hide a room on the left sidebar, it will reappear when a new message is sent with a badge indicating the number of unread messages.
Leaving a patient room means you will no longer receive notifications for the conversation. To leave a room, click the gear icon from right side of the chat room header and select "Leave group." Doing this will leave a note in the patient room that you have left. This makes it easy for everyone to say up to date on who is involved in which patients.
Similarly, joining a patient room will leave a note in the room that this change has occurred. To join a room, select "Browse Patients" from the "+" menu. This will open a list of all patients that have been added to the system. Select a room to preview it, then click "Join" at the bottom of the room. The room will automatically be added to your list on the left sidebar.