As an admin you can edit the members of any team in a running tournament. View the summary screen for the running tournament and you’ll see a list of the teams competing, in addition to a list of their members. To edit your chosen team select the pencil icon on the top right of the team and a popup will open allowing you to add or remove team members. 

Please note the system will not stop you from editing a team to be less than three members but it will lead to issues displaying the current bout order in a match with that team.