When my friend MichaelSur reached level 5, he went to a gym to join Team Instinct, but accidentally chose Valor. He does not have forums yet, so I am posting on his behalf. I think this is because the order "Valor Mystic Instinct" in Pokemon Go made him click the right glass pane which was Valor. Can you please do what you can do to change him. Thank you.
Hey TechMaster85, unfortunately we do not do team changes at this time. Your friend will need to stick with Valor for the time being, sorry for the unfortunate incident.
I was going to suggest to ask a Admin about this issue but apparently he will just have with Valor for now.