The reason everyone is saying you can't "convert" existing game files from a platform to work on another is because it's true. It boils down to how computers, consoles included, run software. Grossly oversimplifying it, you have the console hardware with the console's operating system running on top, and your game interacts with the hardware by "talking" to the operating system. To do so the game has to be coded and compiled with that specific set of hardware and operating system in mind. This process is one-way only, and you cannot get plain code back from compiled files.
In order to port a game to a different platform you'd need the full game code and related assets (which is a very closely-guarded company secret), spend a lot of time and effort modifying it for the platform you want to run it on, get your hands on the compilation toolchain for that platform (another closely-guarded company secret), use that to recompile everything, which could take several days or possibly weeks on a consumer-grade computer, test it on a special console known as a "devkit" (closely-guarded company secret #3) to identify problems, rinse and repeat until it runs properly.
Long story short you'll be much better off getting a proper copy made for the platform you want to run the game on.