1. First login to your Customer Centre account.
2. Click on the Domains menu and select My Domains.
3. Find the domain on which you'd like to create the nameserver and click on the Manage Domain button next to it.
4. Click on the Management Tools tab in the new window that opens and select Register Nameservers.
5. Enter the prefix for the nameserver you want to create without the full domain name in the nameserver column. (e.g ns1, ns2 etc)
6. Enter the IP address of your nameserver in the IP address column
7. Now save changes. That's it. But do keep in mind that DNS changes can take upto 72 hours to propagate across the internet. So your new nameserver may not work immediately.