First you need to log into STORM
Once logged into STORM, you will be taken to the STORM dashboard.
From the STORM dashboard, click on Websites.
Click the Cog icon next to your website to manage your website.
Click on Domains
Click Add Domain
Type in the desired domain name, to use the domain as an alias leave the Redirect box unchecked and click Create Domain
DNS for the alias domain will also need to be pointing at your STORM server, see this guide