Here are the detailed steps for you for adding the nameservers using the WHM -
1. Login to WH using "https://hostname/whm" or "https://ip_of_the_server:2087"
2. Once you will logged in search for the option DNS Functions >> Edit DNS Zone.
3. Select the domain name you want to use, and then click Edit.
4. For the two rows with the menu displaying NS, edit the right-most columns to ns1.your domain name. and ns2.your domain name., respectively.
Please note, you have to enter a "." after your nameserver for working of the DNS properly
5.Add first line in the section 'Add New Entries Below this Line'
First field: Type ns1
Second field: Type 14400
Third field: Select A
Fourth field: Enter your server's IP address (that is IP address associated with the nameserver ns1
Similarly, add the record for ns2
Hope this will help you.