It's easy. 😀
1️⃣ Head to 'My Matches' and select the match you wish to switch teams for, from the 'Upcoming' section
2️⃣ Tap 'My Contests' and select the contest you wish to switch teams for
3️⃣ Tap on 'Leaderboard' and click on the 'Two Arrows' to the right
4️⃣ 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.