- Log in to the Webservices Portal
- Go to Domains -> My Domains
- Locate the domain you wish to modify and click on "Manage Domain" ( )
- Click "Private Nameservers" in the side bar on the left
- Enter the nameserver prefix (e.g. ns1) in the "DNS Host Name" field, and the IP address of your server in the "DNS Host IP" field.
Note: you'd need to perform the above steps for each private/custom nameserver you want to add.