using System;

using System.Linq;

using System.Net.Http;

using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        long od = 1670667197629;

        var doff = DateTimeOffset.FromUnixTimeMilliseconds(od);

        Console.WriteLine(doff.ToUniversalTime());

        Console.WriteLine(ChangeUtcToCest(doff));

    }

​

    public static DateTimeOffset ChangeUtcToCest(DateTimeOffset original)

    {

        TimeZoneInfo cetInfo = TimeZoneInfo.FindSystemTimeZoneById("Europe/Istanbul");

        DateTimeOffset cetTime = TimeZoneInfo.ConvertTime(original, cetInfo);

        return original.Subtract(cetTime.Offset).ToOffset(cetTime.Offset);

    }

}