Here is how to create custom nameservers
Custom Nameservers also called private nameservers, private nameservers actually represent your own domain, Custom nameservers has many benefit, the major benefit is that when you migrate to a new server, your clients will not lose access to their websites due to the change in the DNS (but you have to migrate the existing clients accounts too to the new host.
To create your own custom nameservers, please follow the instructions below
Ask your domain registrar to register your private nameservers by providing the IPs you received in account information email, Each account registrar has provided the enough information on their knowledge base section regarding how to register your private nameservers, you should first search that article in their knowledge base section and follow the instructions. Later when you've done, please go to step 2
Go to cPanel, click on Zone Editor under the Domains section as shown in the image below
Under Zone Editor, find your domain of which you want to create private nameservers and click manage as shown in the image below
Under manage section click on +A record to add a new A record as displayed in the image below
Write NS1 under Name section and leave the field, now next to Record section, you have to enter the IP in the IP4 field (make sure that the IP of NS1 which you are entering in IP4 field is match with the IP you given while registering your private nameservers through your domain registrar) Please note that when you will receive the account information, you can find the IPs next to default nameservers. Next Click ADD RECORD to save the record.
Repeat the step 5 for creating 2nd nameserver and make sure that the IP is matching to your registered nameservers IP for ns2 and click ADD RECORD to save the record.
Follow this step if you are a reseller (have a reseller WHM account)
Go to your WHM and click Basic Webhost Manager Setup as shown in the image below
Click on Explicitly Set the Nameservers option and enter your domain nameservers there which you registered on your domain registrar website and also in DNS zone editor and click save changes