You can purchase specially designed feeding bowls with built-in obstacles such as section dividers that separate his/her food to help greatly help to slow down the quick ingestion of food all at once. These types of bowls encourage your dog to eat around the obstacles, making it extremely difficult, if not impossible for him/her to gobble down a meal full force. You can also place specially made feeding balls (large enough so your dog can’t swallow it) in the bowl as these also create a way to slow down as your dog eats around it. Adding water to dry food also greatly helps to slow down the rapid eating process (and to avoid bloat) and it also ensures extra water in the diet as well.
To train to eat slower at playtime, try a specially made toy which is hollow and allows for dry kibble or treats to be placed inside. The food or treats are slowly released through an opening as he/she plays with it. And always teach your dog to "sit" before you place the food bowl. It not only helps the dog to calm down but reinforces good leadership and focus on you.