When connecting your Slack account to Troops, you will see an OAuth screen that looks something like this:

But what if the Slack group you want to connect to Troops doesn't appear? 

The OAuth will only recognize Slack groups you are signed into on your browser. Go to Slack.com and make sure you are signed into the Group you want to connect.

When you return to Troops, you will be able to choose the Slack group you intended.