I have an app that uses videos from a website of mine, but the videos are configured only for my domain, how do I make my application point to the domain of my site, so that the videos work?
Depends on how you view the videos in your app. If you just embed them, they are not part of your domain but of the app that is running locally, so “file://” or similar.
I can change this “file:?”
No, not really. You could add an iframe where you load a page from your domain that includes the video - but that will have its own problems.
How do I point the url to my domain for the video to work?
As I wrote: you don’t. Local code is local, only way to get something from your domain is to embed via iframe.
If I understand OP correctly, the server serving the videos will only do so to hosts whose reverse DNS maps to something inside
somewhere.com. If that’s the case, whether this will work or not is totally dependent on what the network connection situation of the device is. For general distribution, this is impossible.