I received an email like that and, similarly, it didn't work for me. There is no number, name, department or email to contact. I reached out to the IRS agent that I am currently working with on a client audit. He told me the e-mails went out to everyone but each agent will send their communication through this portal as needed. So, if you are not expecting anything now (and he told me he didn't send me anything), he told me just wait for the next time an agent sends something, and then I will be given the chance to access it again.
This only sounds somewhat accurate but I don't have the energy to pursue this any further. The next time I need it, I will see what happens.