By default, clients hosted on your reseller account could see Anomica's nameservers if they look. Private, branded nameservers make sure the only name they ever see is yours.
Get your nameserver IPs
In WHM, go to Basic WebHost Manager Setup → Nameservers. This shows the IP addresses your custom nameservers need to point at.
Register two hostnames at your registrar
Create host records like ns1.yourbrand.com and ns2.yourbrand.com pointing at those IPs, this is sometimes called a "glue record" since the hostname lives inside the domain it also serves.
Add them in WHM
Back in Basic WebHost Manager Setup, enter your two new nameserver hostnames and save.
Point your (and your clients') domains at them
Update the nameservers at each domain's registrar to ns1.yourbrand.com and ns2.yourbrand.com instead of Anomica's defaults.
Give it time
Glue records and nameserver changes propagate on the same 24-48 hour window as any other DNS change. Set this up before you onboard your first white-label client, not after.