That's Easy!
- Head to 'My Matches' and select the match you wish to switch teams for, from the 'Upcoming' section
- Tap 'My Contests' and select the contest you wish to switch teams for
- Tap on 'Leaderboard' and click on the 'Two Arrows' to the right
- Uncheck the selected team, check the team you want to switch with, tap on 'Switch Teams', and that's it!
PS: You can switch teams only when you have created more than one team for the contest.