Hello There,
So what happens to that process advised by your colleagues before you – uploading a php file onto X-child’s theme? What’s the aim of that process?
The point of this process is that when the theme gets updated your changes won’t be overwritten.
You need to read the plugin documentation in order to learn how it works.Further customizations from here would be getting into custom development, which is outside the scope of support we can offer. If you need more in depth changes, you may wish to consult with a developer. X is quite extensible with child themes, so there are plenty of possibilities.
Thanks for understanding.