Hi Owen,
As Chance was suggesting you’ll need to setup some UVs in Max/Blender or a 3d Modeling software for the most part.
The problem isn’t that the UVs are wrong though, it’s that you need a second UV for lightmaps. You may be aware of them or not, but these are important for Static objects because lighting information will be baked into a texture that gives great shadows with zero performance hit at run-time.
If you don’t want to download a larger program like Blender or Max you can give RoadKill UV a try. RoadKill UV website.
I’ve recommended this for other users as well and they’ve seemed to get some use out of it. It’s a way to edit the UVs without needing an entire modeling suite and it’s simple enough to learn, especially for just laying out a simple lightmap UV.
Here is the intro vid for it just to see if it’s something you may be interested in.
For some more information that may be handy for whatever program you decide to use for your lightmap UV layout, World of Level Design has a comprehensive tutorial series for lightmapping in Unreal.
These tutorials are from UDK/UE3 but they are still relevant to UE4.
World of Level Design: Lightmapping
If you have any questions feel free to ask!