Examine the spit-up on the couch to determine if it has dried. If so, scrape the dried stain with a butter knife to remove it.
Blot wet spit-up off the couch with a sponge or washcloth. Don't rub the stain or press too hard.
Dampen a washcloth with water. Sprinkle baking soda onto the washcloth and blot the spit-up. The baking soda removes the stain and absorbs the odor.
Blot dry cleaning solvent onto the couch if the spit-up remains. Blot until the couch absorbs the solvent and continue applying it until the stain disappears.