usually pumpkin added to the regular food does the trick within a few hours. you don't need a whole lot, 1-2 heaping teaspoons per meal are usually enough already. however, it's not something that works on all dogs, if it doesn't, mashed banana is another option.
yogurt is good, especially if it has live cultures, but don't give too much.
i wouldn't feed any science diet products, they are just artificial crap with lots of chemicals. if a dog really has a bad digestive upset, a bland diet of boiled chicken and white rice is good.