It's possible to leave a team and join another team, but do you really want to do that?
As with most game play, Teams are formed before the Challenge starts. If you need to change Teams before the Challenge start, there's no significant penalty.
Once the Challenge starts, we encourage you to stick with your team. If you decide to leave your team and join another, your original team will keep the points you've earned while on that team. You will have to start over with points and any you earn after you switch will be counted for your new team.
As the end of the Challenge approaches, no more switches are allowed.
Still want to switch? Here's how:
1) Go to the Info section of your Challenge and tap on the Member Button
2) Scroll to find the Team you want to Join and tap the Join Button. You'll be asked to Confirm if you want to Switch Teams and reminded that your points will start over. Tap Switch to Confirm.
3) If you want to create a new Team instead of joining an existing Team, you'll have to Leave the Challenge and then re-join in order to Create a New Team.