1. Browse to System→ Access Control→ users
2. Click on edit the group and then on search
3. Add group members by clicking on the plus in the search results

You can also add them when you create a new subscriber.

1. Browse to Subscriber → create new →advanced options
2. Select the correct group

Or you can go subscriber overview

1. Browse to Subscribers → overview → choose the subscriber → edit → update
2. Change the group and click on update

• Create a group