Backing up a bit
Let's say you wanted to make a game adaptaion of the movie "REC"
Then you would contact the company who owns the rights to the movie. And you would negotiate a deal with them. And they would license you the game rights to their IP.
If another company has already acquired those rights, you would still get in touch with whoever has the rights and negotiate a deal, typically offering money or services or brand recognition, assuming you've got some of those.
Usually these are deals measured in millions of dollars. Subcontracting deals, where you subcontract with whoever already acquired the game rights, are often measured in hundreds of thousands.
Aww, Ninja'd by Graelig