If you want to delete a team (and you’re the team owner), go to the team name and click More options > Delete the team. Your team will be permanently removed.
Remember: Deleting a team also removes the team mailbox and calendar from Exchange.
Team owners and IT admins can recover deleted teams for up to 30 days. For more info, see Restore a deleted Office 365 Group.
Team owners can delete a team in the desktop or web app.