Access USB Device on Network Device

[Fickp]

Hi,
I have a PC connected via Ethernet to a internet gateway ( Telstra T-Max) with a HDD connected to the USB port on the gateway, From the PC I can map a drive to the USB device. On a laptop connected via Wi-Fi and is connected to the Home Group, I can see the PC shared items and the Telstra gateway in the network locations. I cannot map a drive on the laptop to the Telstra gateway. I want to backup the laptop to the HDD on the gateway USB port.

Any help would be appreciated