I'm sorry, but as I wrote you privately, I cannot log into, and work on, servers that don't belong to us, unless you have a work agreement and payment arrangements in place.
It's quite simple; you just create a new domain, with the subdomain name.
If you're a user without the ability to add another domain you have to ask your hosting company to set your account so you can do that. Your hosting company may not allow it (in which case you'd have to create a new account for a new domain) or may charge you something for it.
Jeff