Great Pictures. Thanks.
I was expecting a much worse lesion
It is pretty far forward so I am not so sure it is an inflamed, or infected, elbow callous. It looks more like a scratch that has become infected. Or a "hot spot" which is localized area of infection.
I do think you can treat it at home.
If you go to the drug store, you can buy some "betadine" which is an antibacterial skin cleanser in the first aid aisle. It is a brown liquid in a bottle. Clean the wound with the betadine twice a day until the scab is gone.
When it is dry, apply neosporin antibacterial cream mixed with hydrocortisone cream 50:50. It is not toxic if he licks it but if he does, then put a bandage, or e-collar, on him.
It should be noticeably improved by Tuesday. It will take about 10-14 days to heal.
If it is not healing, or it gets worse, then he should see a vet.
I hope this helps.