There are two ways to reset the router. The first is to perform the hard reset using the reset button. Another way to reset AT&T fiber router is through the web interface. Let’s have a look at the steps.
Steps to reset ATT router:
 Open the web browser and type 192.168.1.254 in the URL section.
 The AT&T login page would open up and you would require entering the default credentials, if not changed.
 Depending on the model you are currently using there should be an option to “reset your system” in the home page
 Select reset and your device should begin to reboot.