ATT Account Transfer - How to load new HBOMax account info?

I transferred the ATT Internet Account for the house from my housemate, and now I get a message that my HBOMax account has expired because my Roku and Amazon Fire Devices still see the old account info.  How do I log-in to HBOMax on these devices with my new ATT Account information and get to use my HBOMax subscription that is part of my upgraded internet service (Uverse 1000)?