From the description that you have given, it could have been an abscess or a boil. As it has already ruptured and drained, ask your friend to clean the area with betadine
or savlon and apply an antibacterial cream like mupirocin
or fusidic acid
. If the lesion is still painful, he might take an antiinflammatory painkiller like ibuprofen
. Also if the lesion is big, a course of oral antibiotic might be required for complete healing and resolution. Hope that answers your query. Take care.