[{"_id":ObjectId("5b36c7fdd515e80009e7cc84"),"code":"1","file":{"dates":{"start":ISODate("2018-06-11T22:00:00.000Z"),"end":ISODate("2018-06-11T22:00:00.000Z")}}},{"_id":ObjectId("5b36c7ffd515e80009e7cf03"),"code":"15","file":{"dates":{"start":ISODate("2018-09-02T22:00:00.000Z"),"end":ISODate("2019-09-26T22:00:00.000Z")}}}]

db.collection.update({},[{"$set":{"file.dates.start":{"$dateAdd":{"startDate":"$file.dates.start","unit":"hour","amount":2}},"file.dates.end":{"$dateAdd":{"startDate":"$file.dates.end","unit":"hour","amount":2}}}}],{multi:true})