Once you have determined that your dog's allergies are food related and are choosing an appropriate diet for them then fresh dog food is a good place to start. Many tinned and kibble commercial diets contain a lot of processed ingredients which may contribute to your dog's symptoms.
Some commercial foods also change recipes depending on availability of ingredients meaning you may end up feeding your dog something they are allergic to without knowing it. Dog food labels can be quite vague and a food only has to contain 4% of an ingredient to be labelled as 'with chicken meat' or 'with beef'. Fresh dog food such as PetsLoveFresh contains simple ingredients that are clearly labelled (including a high quality protein) and without any preservatives (which is why the food is frozen when delivered).