[{"_id":"12345","items":[{"id":"A1","name":"Item One","status":"active"},{"id":"A2","name":"Item Two","status":"pending"},{"id":"A3","name":"Item Three","status":"active"},{"id":"A2","name":"Item four","status":"pending"}]}]

db.collection.update({"_id":"12345"},{"$set":{"items.$[elem].status":"completed"}},{"arrayFilters":[{"elem.id":"A2"}]})