Just unpack the zipped folder into your AppData/Local/PhantomBrigade/Mods folder and enable on the mods menu
AppData is normally a hidden folder if you have issues finding it, type in Microsoft system search bar: show hidden files and enable it.
The full path should be  C:\Users\Name\AppData\Local\PhantomBrigade\Mods\Mark Oskar Liveries\ConfigOverrides\DataDecomposed\Equipment\Liveries
To enable a mod you need to switch it from left panel into the right with arrows.