Are you trying to get rid of the tethering or activate it? If you are paying for a tethered plan then you just use VZ Access manager to connect to the phone or disconnect. You don't need a phone number to put in... VZ Access manager makes the call for you to connect the phone. It also installs the driver for the phone as well.
If you need VZ Access manager you can download it from Verizons site. If you can't find it call Tech support and they will navigate you to the download page.