db={"films":[{_id:ObjectId("634aa49f98e3a05346dd2327"),filmName:"Film number 1",episodes:[{episodeName:"Testing 1",slugEpisode:"testing-1",_id:ObjectId("6351395c17f08335f1dabfc9")},{episodeName:"Testing 2",slugEpisode:"testing-2",_id:ObjectId("6351399d9a2533b9be1cbab0")},],},{_id:ObjectId("634aa4cc98e3a05346dd232a"),filmName:"Film number 2",episodes:[{episodeName:"Something 1",slugEpisode:"something-1",_id:ObjectId("6367cce66d6b85442f850b3a")},{episodeName:"Something 2",slugEpisode:"something-2",_id:ObjectId("6367cd0e6d6b85442f850b3e")},],}]}

db.films.update({"_id":ObjectId("634aa4cc98e3a05346dd232a"),"episodes._id":ObjectId("6367cd0e6d6b85442f850b3e")},{"$set":{"episodes.$.episodeName":"Something Two"}})