At this point in time, we do not have the ability to adjust your account to an org account. This is something that our team is actively working towards internally, but I do not have a timeline yet.
In the meantime, the best thing for you to do would be to create a new Twitter account and apply again. I might be able to accelerate your application since you’ve already been approved, so do let me know if you decide to go this route.
Very sorry for the inconvenience. Improvements are on the way!