What a terrible user interface! I found a way after about 2 hours, if you have the TurboTax Live "full service" option.
If you've scheduled an appointment already, check your email for the confirmation. In that email, youll find a link to change it. Click that link, and choose a new time. After you confirm the new appointment, you'll see an option to cancel it entirely. Cancel it.
Now, refresh turbotax. You'll see an option to "do you own taxes" -- click that, and you'll be in the lower tier of turbotax live. From there, you can follow the instructions elsewhere to cancel at the end when you file.
