If an Agent has more than one Team, you have to select a Primary Team which is set on the Agent’s profile in Agents > Agent Profiles and will be displayed with a blue flag next to the Primary Team's name.

The Primary Team has two effects:

1. It is the Team used when the Agent selects Assign To My Team from the individual Ticket view in the Agent interface.

2. Some  Automated Actions have an option to assign a Ticket to the ‘current Agent’s Team’; this is the Primary Team.