This article applies to 123-reg servers running Plesk.
This article will explain how you can add a DNS record for a subdomain on your VPS server running Plesk.
Login to your Parallels Plesk Panel.
Click on the Domains link on the left panel.
Click on the Open in Control Panel link for the relevant domain name.
Click on the Website & Domains tab.
Click on the DNS settings icon.
Click on the Add Record icon.
Fill in your DNS record details, adding an * symbol in the Domain name field and click on the Ok button to save the subdomain record.