change subdomain to domain WHMCS

[grpcom]

Hello,

At this time I have the 7.5.1 version of WHMCS and I have created a free product package (hosting) for 14 trial days.

Also, I have configured free subdomains for this test account of my users.

Then, with free hosting and subdomain users can create:

A website with wordpress without limitation.

and they also get a subdomain: example.hostwebfreepage.com

Most services that give users a free trial. They also provide accommodation to create a site and a free subdomain.

At this moment WHMCS I can do all the above, perfect.

But, then the user when buying the service can change the subdomain by its own domain.

Use my domain: mybusiness.com

replace: example.hostwebfreepage.com

example the case of the next video shows it, how the user can connect his domain with the service he bought.

This service allows you to make the change with these simple steps:

(please see the video to see the steps)
https://www.youtube.com/watch?v=wmLWxRvFfjA

Now my big question is:

When my client creates his website with Wordpress and then buy my hosting service a domain of his own and want to replace it with the free subdomain.

I want my client to be able to change the subdomain by his own domain as explained in the previous video, easily and quickly.

But I do not know what is the configuration that I must create within WHMCS so that within the client's account of WHMCS - CPANEL AND WORDPRESS my client's domain is activated.

I feel confused and I do not know what to do with this process of changing from subdomain to domain.

What is the step by step that I must configure? or how should this process be executed or treated with WHMCS?

I'd love to hear your recommendations ...

Thanks in advance!