Cable company "Customer Premises Equipment" normally has provisioning capabilities built in, so that they can be controlled/reconfigured/reset from the upstream provider. You could probably call Spectrum and they can reset for you.

The reason they do all of this is exactly because of the scenario you ran into: people are always forgetting their logins -- and back when modems/routers didn't have remote provisioning, they spent a lot of time and money sending technicians out to physically reset people's equipment.