using System;

​

public class Program

{

    public static void Main()

    {

        String s = "2023-07-03T16:38:58+12:00";

        string r = DateTime.Parse(s).ToUniversalTime().ToString("u").Replace(" ", "T");

        string format = "yyyy-MM-ddTHH:mm:ssK";

        string k = DateTime.Parse(s).ToString(format);

        Console.WriteLine(DateTime.Parse(k)+" "+k);

        Console.WriteLine(DateTime.Parse(s)+" "+s);

        Console.WriteLine("---------------------------------------------------------------------------");

        //var format = "yyyy-MM-ddTHH:mm:ssK";

        var unspecified = new DateTime(2022, 1, 13, 16, 25, 30, DateTimeKind.Unspecified);

        var utc = new DateTime(2022, 1, 13, 16, 25, 30, DateTimeKind.Utc);

        var local = new DateTime(2022, 1, 13, 16, 25, 30, DateTimeKind.Local);

        Console.WriteLine(unspecified.ToString(format));            // 2022-01-13T16:25:30

        Console.WriteLine(utc.ToString(format));                    // 2022-01-13T16:25:30Z

        Console.WriteLine(local.ToString(format));                  // 2022-01-13T16:25:30+06:00

        Console.WriteLine(local.ToString("yyyy-MM-ddTHH:mm:sszz")); // 2022-01-13T16:25:30+06

    }

}