2004 XC70 sat nav disk

[1981George]

Hello, I've recently bought a 2004 XC70 that came with built in satellite navigation but didn't come with any disks. I'd like to get it working again but I'm not sure exactly what I need.
I've seen some replacement disks advertised on ebay such as the one below but the seller warns not to buy if you're sat nav shows 'disc missing' which mine does.

https://www.ebay.co.uk/itm/VOLVO-AST...IAAOSwfr1bsocg

I've pushed the eject button on the sat nav unit and nothing comes out so I assume that there really isn't a disc in there, not that there is a disc present that isn't being recognised by the sat nav unit.
The sat nav unit doesn't have a visible model number but says Volvo navigation system and in the bottom right corner DVD rom.

Assuming that there's nothing wrong with the sat nav except it's missing a disc what do I need to do to get it working?
Many thanks
George