To leave your team, select [Team Members] from the main menu and click [My Profile]; or click your name at the top right corner of the screen and select [My Profile] from the list.
Click the [Edit] button at the right of the Profile section.
Scroll down and click the [Leave team] button at the left bottom section.
If you want to join the team again in the future, you need to be invited again by the team owner.
Even after joining the team again, you will have lost all of your availability settings for that team.
Note: The team owner can’t leave it unless ownership is transferred to another member (details here).