*We recommend to use our NS servers, as they are located in 4 different geographical locations and are designed for high loads. But if you still decide to use your own, this article describes how you can do it
After that in the section of ISPmanger "Server settings " item "Features " add "Name server (DNS) ".
Specify in section "Settings " item "DNS Settings " names of NS servers
Остальное по инструкции от - ISPsystem