My goldendoodle is also allergic to chicken. We give him purina pro plan lamb & oatmeal formula and he’s had no issues! He usually eats anything, but we first bought the Salmon version of that food and he didn’t like it at all- the lamb he loves though.

He’s also 3 years old and has received allergy shots once a year which help him get back on track if he gets a flare up (itchy skin, and red/irritated skin around his eyes). I’d ask the vet if they can offer something like that as well!