Unity Store Assets don't work on Terrains

I have bought bunches of packages of assets with grass, tress, flowers, rocks etc. on the asset store and NONE I mean NONE except for 1 package actually works with Unity Terrain. I get the error "Couldn't be instanced because the prefab contains no valid mesh renderer". I have seen comments about the object being the child of an empty parent, however for the life of me I have not been able to figure out how to fix this. Because they are assets from the asset store I don't have access to the original files to fix it in maya or blender.

This is insane I am only trying to paint grass, trees and rocks.

Any help would be great because I am about to pull my hair out.

Thanks!