A team co-captain can be added in the Admin Panel:
1) Navigate to the campaign's Admin Panel.
2) Click on the People tab and Teams tab under it.
3) Find the team from the list and double click on the record.
4) Click Edit button on the pop-up.
5) Click the drop-down arrow in the Team Captains field.
6) Use Ctrl+Alt+Click to add a co-captain.
7) Click Save to save the changes.
Note: A team captain can make other members co-captain via HQ.