Well, in my opinion, you are not supposed to heal his eyes soon. But there are also many things you can do to relieve the symptom. For example, you can warm the cloth and then put the hot cloth on his eyes. And also, you can get some medicines which have the effect on his eyes. If the symptom is still serious, your friend should go and see a doctor, so that he can get the healing.
At this time, you'd better let your friend not play any more. Getting a elbow in the eyes is such a serious problem which indirectly cause the sequelae if not treated well. You'd better take him to the hospital as soon as possible and let hin accept the doctor's tretment.
Feel pain will be the normal reaction of outside clash. Person will feel uncomfortable in a short term. However, if the pain last over three days, he may need to check his eyes in the doctor. The eyes are such subtle parts of one's body. The clash will lead to blood congestion, retina broken. If the retina is well after hospital check, there will be nothing serious; some anti-inflammation eyes drop may help for the infection prevention.