You don't need to. Little Green Dog is a complete food, so it gives an adult dog everything it needs on its own.

Feed it on its own. Extras bring back the proteins and ingredients that can set a sensitive dog off, and make it hard to tell whether the food is working. Give it at least three to four weeks on its own before you judge it.

The protein in our kibble is hydrolysed chicken, broken down so the immune system doesn't react to it. Ordinary cooked chicken isn't hydrolysed, so it can trigger the reaction the kibble avoids. See Does the food contain chicken?

Pick one plain food your dog already tolerates and keep it to a small share of the bowl. If the itching or tummy trouble comes back, drop the extra first.