A dog usually gets bad breath as a result of bacteria and Tarter on Teeth and in the mouth.
So to get rid of the dogs bad breath you need to get rid of that Tarter and bacteria and the bad breath will go away.
You should use some baking soda and water to make a natural toothpaste that can get rid of the tarter and bacteria on the dogs teeth and in the dogs mouth.
Or you can also buy some specially made dog toothpaste to brush your dogs teeth with to get rid of the tarter and bacteria.
Another option is to feed the dog some carrots and apples which help with the teeth cleaning and also are healthy for the dog.
Feeding the dog some Mint or Parsley can also help with getting rid of your dogs bad breath or even using apple cider vinegar to clean your dogs teeth and tongue with.