When you purchase the device it is configured with default factory settings. The credentials are specified in the manual so that you can access the device and configure it later. In any case, if you face any error. Resetting the device is the best solution. As you do so, it will also
reset Xfinity admin password. Press and hold the reset button for a full factory reset and then go to the settings and restore the password. You can also simply change it by logging in through the default credentials.