There's a great Facebook group Dogs with IBD, colitis and pancreatitis UK.
I joined the end of last year after my dog got very ill.
White fish is a good protein. I buy it frozen in Tesco. When my dog was going thru an Ibd flare I mixed that with white rice, sweet potato. Then very slowly introduced Virbac A2 kibble. This is mainly fish based and is hydrolysed.
I have found adding boiling water to it and letting it soak a much better way of serving it.
She'd been on it dry but had an episode of vomiting (purely from being an excitable dog) after a meal and my vet said to try softening it.
This then made it smell more appetising. I still top it with a little fish.
Throughout all this I found that chicken was a no no. Unfortunately it's the go to for vets but if your dog is still suffering then you have to find a different protein.
The stuff I mentioned is v £££ but I'm now slowly adding in a fish and rice kibble. James wellbeloved.
Another poster mentioned fish and sweet potato, I've got a bag which I might give a couple of mixed in.
I've also heard that Burns kibble is useful.
Hth