Make sure you have already installed Lenny's Mod Loader﻿ and ScripthookRDR2﻿ in order to make this mod work:

Lenny's Mod Loader: https://www.rdr2mods.com/downloads/rdr2/tools/76-lennys-mod-loader-rdr/

ScriptHookRDR2: http://www.dev-c.com/rdr2/scripthookrdr2/

Once you have everything installed, all you gotta do is drop the "Cowboy Outfit Reworked" folder inside of your "lml" folder and you should be done!