Remember that the stomach of a fish is about the size of one of their eyes, so it doesn't take too much to fill them up. Feed only a few flakes at a time and see how much they eat within 2 minutes time. (of course if you have bottom dwellers this would not apply and I would think that you'd be feeding them some type of sinking food) If they devour it all quickly before the 2 minutes are up, give them a tiny bit more. If they eat all of that, it should give you a pretty good indicator of the amount you should be feeding. Never tip the jar or bottle directly over the tank - this is how accidental overfeeding occurs.
If he overfed them recently, I would skip a day or two. It won't hurt them. Then I would go back to your normal feeding schedule, but be sure to monitor the food intake. Good Luck