How do I add a Fortnite .umap and .uasset to UE4?

How do I add a Fortnite .umap and .uasset to UE4? It always says “Failed to import - unknown extension”. So how do I do it cuz I find it dumb that most files in my explorer for UE4 are in the same format.

You can’t as they been packaged and not intended to edit. Data mining and modding breaks some of games EULA (aspecially Fortnite) there for you won’t get any support on that