Drag the main.lua and SWATteam.lua to the scripts folder inside your GTAV directory. 
If you wish to add SWATteam as a module and not overwrite the main.lua, you can add this code to the bottom of your file near the other modules.

function tick()
	if (package.loaded.SWATteam ~= nil) then
		package.loaded.SWATteam = nil
	end
	SWATteam = require "SWATteam"
	SWATteam.tick()