If the dog is in a clean, warm environment, kennel cough starts to go away in a couple of days. If the cough lingers, and doesn't seem to be clearing up, take the dog to the vet, but warn them on the phone that you think it might be kennel cough, so they can take appropriate precautions when you visit.
One of mine had a particularly nasty case of kennel cough when I adopted her. She was sick for a week, over the holidays, and when I took her to the vet, they scheduled her at the end of the day, and we didn't stop at the scale for weighing. The vet thought we should have seen improvement in a week, and put her on antibiotics. Her cough cleared in 24 hours.