Our dog is incontinent. We found out the same way you just did. She was only 3 at the time and otherwise was house trained. It happened a few times, not just on the furniture.
They sell some cleaner stuff at the pet stores that is an enzyme and neutralizes the organic matter, worked well on our old couch.
Our VET prescribed some medication for her which has stopped the problem.
We stopped letting her on the furniture (before we got new stuff) which has stopped the potential for other problems.
It took a while but she stays off now and no more accidents (knock on wood).