After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Navigate to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here). Create the folder if necessary
Move the main folder of the mod from step 1 to the folder you navigated to in step 2.
In case you need a second repeat of instructions: extract the MW2019 AS Val into mod_overrides.
Modern Sights: Extract into mods. Needed for the special Dragunov Scope. If you only plan to use vanilla optics, then Modern Sights is optional.
CAFCW: Extract into mod_overrides.
Not needed if you ony plan to use vanilla optics, but needed if you want custom optics.