By default, we provide the option to add a custom domain on your cloud account. But it will work only with HTTP protocol. In order to use SSL, please add a certificate along with the private key at Administration » System.
The certificate should be generated for your custom subdomain used for the help center or wildcard certificate and key of your main domain.
Sometimes we require to apply your certificate, so you would need to submit a request to our support team.
You can also generate SSL certificate right inside our system on General System settings where you enter the custom domain.