How do I get rid of the oder from cat spray on my couch?

Most pet store sell a product for this called Miracle clean, 1 gal white jug $21. It is a enzyme that consumes the urine but may take 2 or 3 applications.

I'd try the Nature's Miracle (or similar product) first. However, you need to be aware that cat spray (especially from an unneutered male) is considered one of the most difficult odors to get rid of. So, depending on how badly the couch has been sprayed, you may wind up having to get rid of it.