To make the Plesk’s DNS server act as a secondary name server, perform the following steps:
1 – Logged in to Plesk.
2 – Go to Websites & Domains and click the domain name whose DNS settings you want to manage.
3 – Click DNS Settings.
4 – Click Master/Slave to switch DNS server mode.
5 – Click Add Record.
6 – Specify the IP address of the primary (master) DNS server.
7 – Click OK, and then click Update.
Repeat steps from 3 to 7 for each website that needs to have a secondary name server on your server.