Squamous cell carcinomas?

Hello everybody, looking for opinions, advice, and similar experiences.

Our dog got hit by a car last year and was immediately brought to the vet. No broken bones, just swelling. Crated him for weeks, and for the first few weeks we had to assist him to pee as he couldn't do it himself. He experienced a lot of muscle loss in his back legs during this time and it took months to regain this. He is since doing so much better, can run around and do everything he used to do. However, he still has no control over pooping. It just falls out of him when it's ready.

He has gone to all of his vet visits and they cannot find anything wrong, and to help learn what's wrong with his bowels they only suggest bringing him to get an MRI, which would involve us flying him over to another island as there is no MRI machine on our island. They do not think he is experiencing any pain, although my owner's intuition makes me think otherwise and I think he may have nerve pain and some aches.

He is approximately 6 years old (but rescued so we don't know his exact age), neutered, male, 45lbs, pit mix. I am considering starting supplements, but unsure what I should try. He regularly gets vet checkups and seems in good health otherwise. He just cannot control his poops. I want to see if starting supplements will help strengthen that area and help bring him a little more control.

Thank you so much for reading and looking forward to hearing from all of you

Breed is a labrador mix. He was being careless with a sharp end of a bone, and injured his gum.

The injury is looking fine but still looks mildly faint on the cut he had. Was really hard to get a photo of my lab but basically it seems healed but I still suspect its too early for the return to Kibbles.

Been feeding him a bit of soft chicken breast and some canned dog food, and used a bit of soaked Kibble but he doesnt seem to like Kibble as much when its soaked.. Loves it otherwise

Below pic is not mine but looks closest to what my dogs injury looks like now(the right darker gum part)

Would it be too early in this condition to resume Kibbles? Its like his favorite food but I dont wanna see him hurting himself again if its not fully healed yet. Based on what the vet said it should be fine by now but I feel like I need to wait for 3-4 more days..