To add an Operative to a Fire Team left click on their name in the MISSION ROSTER box on the left. Left click on the ADD button of the appropriately colored team. You can change the position of the operatives on each Fire Team by left clicking on the operative and then left clicking on the PROMOTE button.
To change teams once an operative is already assigned, left click on their name and then left click on the ADD button on the new team.
Left click on the right green arrow to proceed to the PLANNING screen.