As far as I remember it contains some prefabricated buildings in form of UE blueprints. You could be able to put them in new map and then convert to static mesh and finally export as FBX.
Update: I’ve looked into it and it contains level named Map_Buildings. There are some prebuilt bunkers in the form of groups. So you may select one of groups and merge it into single static mesh (Actor/Merge Actors), then position and export it. Note that there are also some decals and you probably should remove them before as they will not transfer to other software via FBX correctly.