I helped another member get his Fios router configured - If you read through this post, it is exactly what you need to do - except the UI will be different for your ATT router to get to the correct screens.
If you want to do a Chrome Remote Desktop session with me, I could probably get you configured in a few minutes.
https://chrome.google.com/webstore/detail/chrome-remote-desktop/gbchcmhmhahfdphkhkmpfmihenigjmpp?hl=en
What is the brand and model of the Uverse gateway you have?