Download REUE4SS. The link goes to the releases page which should have the latest experimental release available at the top. At the time of writing this the file is named "UE4SS_v3.0.1-280-g3912ee3.zip" but versions might change in the future (e.g. a future release might be named "UE4SS_v3.0.1-285-g3912ee3.zip". I suggest using the latest experimental release always and keeping it updated since it contains various bug fixes, performance improvements and is updated frequently.
To install REUE4SS you need to extract its .zip archive and then go to where your game is installed and navigate to this path: \Pal\Binaries\Win64. Drop the extracted files here. In the end it should look like this:
\Pal\Binaries\Win64\dwmapi.dll
\Pal\Binaries\Win64\ue4ss
Download the mod. Extract its .zip archive.
Go to where your game is installed and navigate to \Pal\Content\Paks. Make a new folder named "LogicMods" in here if you don't have one already.
Drop NightVision.pak from the .zip archive in here.
In the end it should look like this: \Pal\Content\Paks\LogicMods\NightVision.pak