I am afraid that this is not possible and you are able to create subdomains with your domain only in the hosting account where your domain is placed for the present time. But if you want we can move your domain from your current hosting account to the other one, tjhen you will be able to create the needed subdomain.
If you want to do that, please open a trouble ticket from the hosting account where your domain is hosted, so we will be able to assist you further.
In order to open a new trouble ticket, please use the Control Panel > Help Center section.
If you have any other questions or problems, please let us know.