Sometimes rebooting the router does not help to resolve the issue you are facing and you need to reset it. The following is a method to ATT UVerse router reset. You can reset the router by holding the reset button for 20 seconds. You must wait till the light turns green. Holding the reset button for long enough is important otherwise the router will only reboot and not reset to factory settings.
Read more: https://connectrouter.com/how-to-access-att-router-settings/