If you are currently on a Pro League team and wish to join a Challenger Circuit team (or vice versa), ask the team captain to send you an invite link to the other team
Once you've joined the other team, you will see that team name appear at the top of your nav bar next to the original team you were on.
You may view each team by clicking on the team name
You can learn more about how being on a Pro League & Challenger Circuit team works in the rules
You cannot be on two Challenger Circuit teams at the same time.