Our Cube keys are digital entitlements. Look in the Windows store at your account and see if your device shows up. If it does you should be able to just reinstall Windows using Microsoft’s media creation tool and it should automatically activate. During the installation tell it you don’t have a product key and it will continue.
Just to be safe though, use Clonezilla to take a backup of the previous install so you can restore if it doesn’t activate properly.