How to update array of object in mongodb

i want to update "pharmacy_note" field that has inside of array object my mongodb collection here

{ "_id" : ObjectId("587f477c890202980f693cd7"), "doc_id" : "cf05effe-49ff-4dfc-b286-74469956be6f", "visit_id" : "56d29f560a0acbef475d9810", "pharmacy_name" : "Hospital Pharmacy", "pharmacy_id" : "AB1234", "prescription_items" : [ { "quantity" : 4, "number_of_days" : 2, "reg_price" : 1600, "reason" : "bacterial infections", "instruction" : "Take medicine at the same time each day", "route" : "Oral", "frequency" : "One Time a day", "unit" : "mg", "dose" : "250", "name" : "Cipro", "pharmacy_note" : "this field i want to update", "_id" : ObjectId("587f462a890202980f693be4"), "is_dispensed" : false, "start_date" : ISODate("2017-01-25T18:30:00.000Z") } ], "prescription_generated" : false, "prescribed_date" : ISODate("2017-01-18T10:46:20.885Z"), "prescription_id" : "01348416-d38c-4340-b18d-6b7578ef05e5", "__v" : 0 }

Thanks in advanced...

via Nk Patil