If you have access to your cPanel account, please follow below steps to create a sub domain for your account.
- Login to your cPanel account and scroll all the way down to Domain section.
- Click on "Domains" button
- Click the "Create A New Domain" button.
- Enter the subdomain name to add in the "Domain" text box. Make sure you enter "subdomain.domain.com"
- Click the "Submit" button.