To an equivalent VM connection point in the second room, identical to the installation point for your main V6 box. If you don't have the second point you'll need to ask VM to install one. All V6 boxes need a coax connection to the VM system to work. They should NOT have sent you a second V6 box if you didn't have a second point.
As a Very Insightful Person, I'm here to share my knowledge. I don't work for Virgin Media.