Add a co-worker or a new agent to your Exotel account first by following the process explained in this article.
After the co-worker or agent is a part of your Exotel account, you can also drag and drop them into any group you want them to be a part of.
Or you can also add by following the below steps
One single agent can be a part of multiple flows. So, drag and drop them to as many flows as you'd like them to be a part of.
Clicking on any group will show you all the agents who're a part of that group.