User user= allData.rows.FindIndex(
                                            delegate (User us)
                                            {
                                                    return us.id == 1;
                                            }
                                        )

List<int> list = new List<int>() { 1, 2, 3 };
int index = list.FindIndex(v1 => v1 == 2);
list[index] = 4;