Problem with static mesh's nav volume for AI

I ordered few static meshes from a freelancer, but unfortunately nav volume doesn’t allow my AI go underneath and up to their stairs. Anyone had this issue? What can be done? Please!

Hey,
Check the collision of your assets I think you don’t use mesh collision. (use “complex as simple” or create own collisions)
Currently, you use the default collision. (You can change this in the mesh preview editor)

Thank you so much - it worked!
I am happy, so many objects are now useful for my games! god bless you and your name is written in my game credits!