You can leave a team at any time by going to the team name and clicking More options 
> Leave the team.
Note: You can leave a team on your own, but only an admin can remove you from an organization or an org-wide team.
iOS
Go to the desktop or web app to leave a team.
Android
You can leave a team at any time by tapping Teams 
, going to the team name, and then tapping More options 
> Leave team.