how can I load a mesh from a larger object in resources to put in a skinned mesh renderer at runtime?

I have already figured out how to get it correctly positioned and animated. In the editor I can go to assets, 'spread out' the fbx file, pull out the mesh I need and put it into the Mesh slot in a skinned mesh renderer. I need to know how to do that with script at runtime. I have seen many examples of people using mesh filter, but for some reason this gets an error how ever I try to do it so I think it might be obsolete or just people trying things that doesn't work. it either doesn't compile for me or I get an error at runtime saying that types can't be converted this way. I would prefer if I could to load the mesh directly. I have managed to load the whole fbx object, but I would prefer not to instantiate it at least.