using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

​

namespace Rextester

{

    public class Program

    {

        public static void Main(string[] args)

        {

            DateTime localTime = new DateTime(2023, 03, 09, 10, 00, 00);

            string localDateTimeString = localTime.ToString("O");

            string franceZoneId = "Romance Standard Time";

            TimeZoneInfo easternZone = TimeZoneInfo.FindSystemTimeZoneById(franceZoneId);

            var convertedToUtcDateTime = TimeZoneInfo.ConvertTimeToUtc(localTime, easternZone);

            Console.WriteLine("UTC: {0}  |  ISO String: {1}",convertedToUtcDateTime, convertedToUtcDateTime.ToString("O"));

            Console.WriteLine("Local: {0}  |  ISO String: {1}",localTime, localTime.ToString("O"));

        }

    }

}