Absorb as much of the spilled vinegar off the couch by blotting with several paper towels. Continue blotting until you can no longer absorb any more vinegar.
Add 2/3 cup of rubbing alcohol to a small container. Mix 1 tbsp. of white vinegar with the alcohol using a spoon to stir the two liquids together. Moisten a lint-free cloth in the mixture.
Blot the vinegar stain with the cloth for several seconds, and then blot the damp stain immediately with a dry lint-free cloth.
Continue alternating between blotting the stain with the damp cloth and the dry cloth until the vinegar stain is no longer present.
Remove the mixture residue off the couch with a clean cloth dipped in water.