To add a Team Lead, go to the Teams & People page, select "Team Settings" from the menu on the corresponding team, and then select Permissions in the left-hand menu.
Select the team member(s) you'd like to designate as Team Leads and click "Save."
Team Leads can:
Update team settings
Update team visibility
Add/remove users to a team
Designate other users as Team Leads
Team Leads cannot:
Delete a user
Access account settings
Deactivate or reactivate a team
Deactivate themselves
Remove themselves as Team Leads
Log in if they are deactivated from the teams they are on