Hi Danielle,
You can try treating him at home first, but you may have to take him to see a vet.
Take saline solution (the type that you use on contact lenses) or one teaspoon of boric acid mixed with one half cup of cooled, boiled water, and use that to cleanse the eye. You can wipe the eye with a wash cloth dipped in warm (not hot) water. Do this 3 times a day, and give him a few days to see if it improves.
If the redness is still there by Monday, you should take him to a vet for antibiotics to clear up the infection.
Let me know if you have any other questions.
Susan