Buy nasal blower for pediatric use and keep cleaning nose secretion. And use that nasal drop it will gradually settle ,if not then see a Dr. ask if needs further medication.
Diploma in Child Health (DCH), F.I.A.M.S. (Pediatrics)
Pediatrician, Muzaffarnagar
You have not mentioned medicines he is taking. He is already under care of pediatrician. You may try Saline nasal drops to be instilled 2-3 drops in each nostrils 3-4 times in a day if no nasal drop is being used.