Making a mesh collider

Hey guys Im having a issue with making a mesh collider

When I create a new mesh collider I notice that it doesn't allow me to change the scale or rotation of the collider

I made a separate mesh collider than the mesh of the model being used.

I tried inserting the mesh into my scene and size it just how I want it and then save it as a prefab and then try using that prefab as the mesh for the collider but unity doesn't accept that.

Anyone have any ideas on this thanks.