Diet change is always the easiest to try first.
I personally feed prey model raw. So I know exactly what my dog is eating. Grinds tend to add "supplements". I found what works best for my guy. Some dogs do well on kibble, just have to find the right one. Some dogs do OK on grinds. It's essentially a process of elimination.
"i can explain it to you, but i can't understand it for you."