If your router is from Xfinity you can find your default SSID and network password on a label on its side or bottom panel. This label will contain SSIDs of your 5GHZ and 2.4GHZ networks and default password to them. If you or service technician hadn't changed default SSID settings then these credentials will work with your Wi-Fi network.
If your router is using default SSID and credentials, we recommend to change password for your Wi-Fi network. Otherwise it is wide open for attacks in case someone gets access to your default password.
Please note that credentials described above will not work for Xfinity Gateway administration tool. This interface is accessible by typing http://10.0.0.1/ in your browser address bar. To login into Xfinity Gateway admin tool you can try to use default login credentials.
Password: password (case sensitive)
Using Xfinity Gateway you can access and modify credentials for your Wi-Fi network. To do this login to Xfinity Gateway admin tool. Select "Gateway" in the left navigation menu, then select "Connection" and then "WiFi". You will see SSID of your network in "Private WiFi Network" section. Click edit on a network which you want to change. Type new password and click "Save Setings".