Importing Problem: Imported .dae model have some missing parts

I imported a .dae model and it has some missing parts. How can I fix this?

I don’t have time to create the missing parts.

Hard to say anything without access to the Collada file.
If the file itself is damaged/faulty, there’s not much you can do. Does the Collada file open correctly in other 3D software? Are other file formats available?

Try importing into meshlab and then exorting as .obj file.

Oh I have forgotten about this one. I’ll try what you guys suggested. It is weird though that it imported fine on Unity 5. But I need to import it in Blender so I can rig it.