Your vet is best placed to advise you. For severely overweight animals there are prescription diets available which are very calorie-restricted and these are really helpful, but many owners, with commitment, succeed in getting their pet to lose weight without changing their basic diet at all. Most overweight dogs are getting too much food as well as excess treats, so simply cutting down the amount is all that is required.
I usually advise owners to half the dog's daily food intake (bearing in mind many of the dogs I see are extremely obese) and then split that ration into three small meals which can be bulked out with cabbage if required. Cucumber or carrot pieces make great treats.
If there isn't a great deal of weight to lose, Chappie is a good choice. But you really need a bit of guidance from your vet.
I'm sure you've sorted this already but I'm new here!!!
Our Lurcher suddenly started putting on weight one year and we couldn't figure out why. The vet said it was because she was getting older and we were still feeding her working dog food. We changed her to older dog food (wagg complete is good and good price too) and she's been fine ever since!
The other thing is monitor what everyone is feeding the dog. You may think he/she is only getting a little treat from you but if 6 people are giving little treats it mounts up!!!