Login to WHM

Under the section Server Configuration click Basic cPanel/WHM Setup

Next to Primary Nameserver enter your private name server (ex ns1.yourdomain.com)

Next to Secondary Nameserver enter your second private name server (ex. ns2.yourdomain.com)

Then click Add an A entry for this nameserver for both name servers.

Your name servers are now configured in WHM and ready to use.

Note: You must also create the name servers at your domain register