As the event administrator, you are able to assign someone as team captain.
Log in to your account and select the event you wish to work with.
Select View Participants.
Choose the fundraiser that you wish to make team captain.
You can also remove from the team or change team.
Note: You are only able to add, change or remove a fundraiser from a team if they have created a personal fundraising page. If they have not created their personal page, you will need to provide the fundraiser with their create page URL link which can be found in your Participant Details Report in the Create Page URL column.