You should check with the provider that there service would work with a CName record. A CName simply gets the IP of the Full Qualified Domain Name you point the CName record at, it does not forward to that domain. Most services work on host headers, so unless the service is setup to work with your sub domain it will most likely not work by setting up the CName record.
If you do wish to setup a CName record on our systems there are two ways to do this depending on the service you have from us.
If the domain is registered through us you can use the Domain Manager in your Client Area account to edit the details of the domain where you will find a DNS Editor that can be used to create the CName record.
If you have a hosting package with us you can go to the Domains section in your control panel, where you can edit the details of the domain name where you can find a DNS Editor that can be used to create the CName record.