Set up a subdomain for a new site - domain is registered elsewhere

Hi all,

I'm currently on the launch plan so can have 2 websites hosted on my account. I have 1 setup already however I want to make a second one.

I have a website hosted elsewhere (eg. mydomain.com) and I now want to create sub.mydomain.com and host it on inmotion. The domain is not registered with inmotion.

What steps do I need to take to get the site set up? Do I first need to change some domain settings or can I do it all through the cpanel?

Thanks a lot for reading - I appreciate the help.

James