REMINDER: You can only leave a group if it's settings allows it. If your group settings is "locked", once first game tips off Friday March 19th 12noon EST, you will NOT be able to leave your group. You can always leave a group prior to tipoff.
To quit a Tournament Challenge group,
Visit your group page and select "Leave Group"
Select the entry you wish to leave the group
If you left the group successfully, you will see a banner that says so.