You don’t, and here’s why/what you should do instead.
Copy/Pasting a games narrative into a screenplay is almost always doomed to fail for many reasons, the largest being that games are an interactive medium. The gap between major narrative points in games are full of…something that isn’t directly related to the narrative advancing. Exploration, combat, puzzles, collecting items, getting from Point A to Point B, etc. There’s simply no good way to write those things to feel the way they do in-game. More importantly, as I already stated, you shouldn’t try to.
So what should you do? Look at the larger story and lore that the game takes place in. I can’t think of a single game that simply begins and ends with the start of said game, and it’s conclusion.
- Gears of War
Sure, chainsaw-bayonets and gun-wielding human-shaped monsters are cool…but it’s pretty hard to take all that seriously while playing it, trying to convert that into a movie or a show would be a waste of money and other resources. Money and resources that could be used to convey a much more compelling story within the larger overall story GoW.
Like The "Birthing Farms"
From the Wiki
“The Birthing Creche, or Farms, were a series of breeding farms where women were impregnated to help repopulate the Human race. Under the Fortification Act, all males were placed in the Armed Services and women in “war work”. Some women could choose (or be forced) to go to the farms. Women who were impregnated were given extra rations over a non serving male. Doctors gave girls hormones at age ten so they could begin menstruation and were able to be impregnated. Many barren girls were abused in the farms and most of them left traumatized…”
This isn’t the best example admittedly, because it’s basically just The Handmaid’s Tale, but instead of a hyper-militant Fascist Theocracy where women are just objects, by law. it’s a hyper-militant Fascist, Secular Autocracy. Not the best example, but I think it gets the point I’m trying to make well enough.
TL;DR: Trying to adapt the vague concepts of games and/or their stories directly = bad. Trying to adapt individual plot points, themes, aesthetics, lore, etc = good.
But that just one persons opinion.