Reauthorisation problem

I have digital editions but need to erase authorisation and reauthorise it to make my Kobo e-reader work as it has stopped allowing DRM protected books from the library (Kobo said this is what I need to do).

The account is registered to an old email I no longer use.

Although I updated my email and password the pop up box in digital editions is only recognising my old email and wont let me change it. And I cannot remember the password I used with Digital Editions. It won't let me enter my new email or password. I am working on a Mac. Any idea how to solve this?