Firstly you may need to know the term resold account.
Generally a customer exist under a reseller account will be referred as a resold account.
Explore Feature Manager in WHM
Feature Manager is an interface that allows creating a list of features that will be available for particular cPanel accounts.
Create New Package in WHM
You may start creating new packages in WHM . A hosting package is simply a set of functions, limitations, and resources each cPanel account may have within a Reseller Hosting Account.
Add a New DNS Zone in WHM
A DNS Zone is an administrative portion of DNS settings that belongs to a domain name.
In other words, every domain name has certain DNS settings and in order to keep them all together, a DNS Zone file was designed. A DNS Zone can be easily added/ managed via WHM >> DNS Zone menu.
Setting Up Private Nameservers in WHM
Setting up your own private nameservers on a cPanel server has many benefits, most importantly enabling all of cPanel’s built in DNS tools.
Many resellers choose to have their own name servers for appearance or branding reasons.
May refer to this guide for setting your private nameserver in WHM