Here is the form you are looking for: go to Asana Support - Help Center • Asana, into “Having Trouble With” and then below you will find a “Still can’t find an answer” button.
Sorry for the confusion here! As @Bastien_Siebman mentioned our support team will be able to assist you to fix this but let me give you some context in the meantime:
A Workspace is essentially a self-contained team; when converting a Workspace into an Organisation, the Workspace automatically becomes the first team of the Organisation. When the Workspace is premium, the premium subscription automatically travels with the Workspace and become a Premium team; this is why when you create a new team you’re prompted to upgrade your whole Organization.
Our support team will be able to move your current premium plan to the Organization level, allowing you to benefit from your premium plan across all your teams.
Hope this helps, but should you have any follow-up questions, please let me know, I’ll be more than happy to help!