[{"_id":{"$oid":"63ef95daf324e5a26354eb61"},"idCarga":"6182944","12121212121212":{"info1":"hello","info2":"goodbye"},"13131313131313":{"info1":"hello","info2":"goodbye"}}]

db.collection.update({"_id":ObjectId("63ef95daf324e5a26354eb61")},[{$set:{"15151515151515":{"$ifNull":["$15151515151515",{"info1":"hello","info2":"friend"}]}}}])