To add an additional domain to your hosting account, you must first enter your cPanel, then you will be directed to the Domains section
There you will add the additional domain without including the prefixes "htttp: //" or "https: //" or "www"
Likewise in the same section of Domains, you will find the one of subdomains
What you should do is add the name that the new subdomain will carry
For a better explanation you can see our video tutorial: