Hi thanks for your question.
The swelling wrist could be due muscle sparain or haematoma
(collection of blood under muscleor skin) or it could be due fracture
of any bone involved in wrist joint.
The best thing would be to consult a physician,but if you can find one, get X Ray
of his wrist joint done to rule out or confirm fracture.
If there is fracture of any bone on X Ray,then he needs orthopediac consultation.
If X Ray rule out any fracture,then he needs antibiotic ,analgesic
anti inflammatory (pain killer) drugs.
Keep his arm elevated,this will help in reducing edema.
Hope this answers your question.