To leave a chat room, click the three dot menu, then Leave room (Figure 1):
Figure 1 Leave room
You can also leave a chat room from the Chat details menu (Figure 2):
Figure 2 Leave room
If the option to leave the room is not visible, it means you’re a chat room owner and you must first remove yourself as an owner before you can leave.
To do this, from Chat details click on Members. From the list, locate your name and hover over it. Click the three dot menu, then click Remove as owner (Figure 3):
Figure 3 Remove as owner
Once you're no longer a chat room owner, you can leave the chat room using the steps above.
Note: A chat room must have another owner before you can remove yourself as an owner and leave.