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.
Deleting a team also removes the team mailbox and calendar from Exchange.
The corresponding SharePoint site and all its files will also be deleted.
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.