You can either reset the router using the web interface if you remember the login credentials. Most of the routers have the reset button where you can simply press the button and reset the device. Another way of how to reset AT&T fiber router is as follows. Steps to reset ATT router: • Locate the reset button on the router. It is usually present at the rear end of the router. • Then, press and hold the reset button for 10-15 seconds. • Release the button when you see the lights on the router starts flickering. • The router will restart and set back to default settings.