https://techcrunch.com/2019/02/21/pokemon-go-will-soon-let-you-change-teams-for-about-8-also-instinct-rules/

Early on in Pokémon GO, you’re asked to make a decision: Which team do you want to be on? Instinct (Yellow)? Valor (Red)? Mystic (Blue)?

The question comes a bit out of the blue. Especially amongst those who started early and have stuck with the game, it’s not uncommon to hear people grumble about how they wish they’d chosen differently. But once you choose, it’s final; changing teams means making a whole new account and starting the grind from Level 1. Well, until now.