You need to know why your dog is chewing on it's foot. If the reason is not resolved what ever you put on the foot your dog will probably try to remove it. You could put Neosporin ointment on the wound and lightly bandage the foot. Make sure you do not bandage the foot too tightly or else the foot can swell. If allergies are causing the skin to get warm, damp, and infected then you might want to try Derma-IonX to help heal the skin. Derma-IonX which is an oral homeopathic product stimulates the enzyme systems in the body which reduces itching and inflammation , promotes healing of the skin and helps with assimilation of nutritional components in diet and supplements. The supplements I use along with it include digestive enzymes, probiotics, vitamin C, MSM, and fish oil. Together with Derma-IonX it produces a synergistic effect for a faster response. It can also be used topically if there are troublesome spots on the skin. I would also suggest that you give your dog only filtered water for drinking and bathing if your water contains chlorine or fluoride. For the dietary modifications you might want to try a grain free diet for a while.
If the infection is quite bad you will need to see your veterinarian for oral antibiotics. Sometimes it can be helpful to shave the foot and clean it well. Your veterinarian can probably do this easier than you can.
Please feel free to contact us again if you have any other questions.