If it is not listed in the registrar module, a module needs to be created for the registrar.
You can either do this on your own or contact WHMCS and the registrar to see that whether they are able to develop it.
If you are not familiar with programming knowledge as well as your registrar's API, I will advise you to contact the developer of WHMCS to develop this module for you. There will definitely be a charge for it if your registar's module is not in their to-do-list.
WHM Doesn't support Custom Registrar modules, Also custom development from WHM is costly and I'm talking about WAY Up there. You can add it to their suggestions forum and they might add it in the future or possibly add it to 4.1.0 since its still Beta