Since this process differs from registrar to registrar, it's difficult for us to give you a full walkthrough. The best place to start is to look at the online control panel of your Registrar and see if you can find it there. If you can't find the area to register nameservers, you may want to contact your registrar for help with their system.
If worse comes to worse, one of our support personel will add the nameservers for you, if possible.
