Im having invisible triangles on imported static meshes from blender

I’m working on a video game about world war one, so I started to make a trench model, however after I finished it in blender, I imported it to unreal, only issue is I get invisible triangles all over the place. I looked into this issue for a few hours & haven’t found anything that has helped. Here are some of the images to show what I’m talking about. Any help with this would be greatly appreciated!