I've never done it but I believe if you log in to the Openspot, select the Connectors tab and under "autoconnect" you can have your Openspot connect to a specific talkgroup upon startup. It wasn't exactly as I recalled.
If you key up on a Group Call talk group (such as 3100/Nationwide for Brandmeister) you should hear activity if you wait for a while. You should also see the activity under the Status tab.