User blog comment:MisterWoodhouse/Uniting the Fandom and Gamepedia login systems/@comment-168424-20200720174823/@comment-1824272-20200721210832

You're looking for this link: https://www.twitch.tv/user/delete-account

Obviously, I would recommend holding off on this until the merge is complete and you can confirm you can log in to your Gamepedia account without any problems.