If your nameservers are set to the shared Plesk server you are one then you can log into Plesk to add a DNS record.

1. Log into Plesk with your username and password
2. Select the "Websites and Domains Tab"
3. Select the domain you would like to add a DNS records for
4. Click on "DNS settings"
5. Click the "Add record" button
6. Add the record that you require and click "OK"
7. Click "Update" on the yellow information bar at the top of the page to apply the DNS changes or "Revert" to discard any changes