Hello, friend!
HG8245W5-6T is a customized product for carriers.
According to your question description, the root account is the default login account and password of the device, not the administrator account and password of the device. To obtain the administrator account and password, contact your ISP.
In addition, if devices are customized by ISPs, users may be restricted from configuring WAN-related parameters. Generally, home networks are connected to ISP networks. If you need to configure WANs or modify WAN-related parameters, you can obtain solutions from ISPs to prevent network interruption caused by incorrect configurations.
Thanks!