Being on the "wrong team" is not a unique problem for Pokemon GO. Players often join the Horde in World of Warcraft before finding out their friends are in the Alliance. Often, a gamer will get through a game only to find that their friends are on another server and joining them means starting over.
Thankfully, while there are important factors to consider when changing teams in Pokemon GO, it is possible to do so and only takes a few seconds. Please read through the warning and then, if certain, go ahead to the final section to complete the switch.
An Important Warning
When completing this process, any Pokemon in Gyms will have their remote berry feeding cease. These creatures will be put into storage, but only after they are defeated or if players visit the Gym to retrieve them. Trainers will also receive no Gym rewards for defending the location. Other items still around, like the new incense, will remain in the Bag.
It's also important to note that changing teams can't be done more than once per year. If trainers change sides, they'll need to wait 365 days before they can change teams again. Be absolutely certain before continuing on to the next step, otherwise changing teams will require either a new account or a lot of waiting.
Changing Teams
Open the Shop and purchase a Team Medallion. This item is a one-time use item and will disappear after a single use, meaning players who want to change again in a year will need to purchase the Team Medallion all over again.
After this, open the Bag to find the Team Medallion. Tap it to use it and choose which team to join. Being on the right team makes Pokemon GO a multiplayer mobile game unlike any other.
Pokemon GO is available now on Android and iOS devices.