Swarm Agent: Compile Unreal Lightmass

I’m trying to package my small level, but every time I attempt it, I get the error message that you see in the question title. How on Earth do I Compile the Unreal lightmass? Note, the Lightmass files don’t even exist in the program file, and I downloaded UE4 from the Epic Games Launcher. Also, if I have to reinstall, does that mean I will lose the project files I already have?