Here tutorial step by step How to Create a DNS template on Virtualmin
1. Login into virtualmin panel
2. And go to Virtualmin tab,
3. Select Dropdown menu System Settings
4. And Click the Server Templates
5. Select the name of the template on the right, for example templates Default Settings,
6. On the Edit drop-down menu template section, select a DNS BIND Domain
7. Scroll down, in part Additional box manually configured nameservers, Please insert the nameserver for example ns1.mydomain.com and ns2.mydomain.com
8. And then click save