How to change the invalid email address in Digital Editions?

I get the "Error! Check Activation" error when I try to add a Kobo ebook, URLLink.acsm, to my library. I am told that I must deactivate DE and then reactivate it but I can't because I don't remember my password and can't reset it because the email address is no longer valid.

So, how can I change my email address to complete this task to add to my library?

Why, oh why, do software companies not provide an easier way to fix such conditions?