kind of a strange question "lost the configuration of your modem".
In cable world, a modem for a customer gets provisioned at ISP ( Telenet). This ensures that proper services (speed, TV, phone, ...) is being provisioned in the modem config file, which you basically can't "lose" as coming from central, not from local storage on modem.
So if modem loses everything, that would mean that provisioning got lost completely, and would also mean no-one here will be able to help you.
But how/where do you see that you need to enter some id ?