22 minutes ago, kpopguy said:

So I have this 3d fps developed, mostly abandoned project, it was on Steam around 2016 (it still is...). I decided I wanted to sell the source code to someone who can handle it and is willing to use it somehow...yes I know about 3d model rights and yes there is a reason why I am selling. Thanks in advance! 

You either need to contact someone and pitch the sale of the game, but you'll have to strip anything that you don't have rights to, or if they're single licenses (non-transferable, ect...).

Beyond that, you could sell it on the asset store as a FPS template if it's decent enough. If you don't want to use the asset store then you're forced to find out how to market the sale, and here wouldn't be the place.

Best of luck.