Just to provide more information now that the topic has been resolved.
Despite being "Admin" I could not access any chat windows to get support via Customer Care and was caught in a quasi doom-loop of support/help/contact-us tab clicks, all returning to the same page. - As suggested, I switched browser, from Google Chrome to Microsoft Edge and was able access a chat session.
To answer my original question, unlike on the example help screens on the support/troubleshooting links, there was no box where I could insert the Tax ID. Resolving this via the Customer Care chat, a member of Adobe reached out and sent me an email for me to upload the information - which I did. Without using the chat session I would not have been able to resolve this matter.
Thanks Experts. I hope this information helps fellow users.