How do I convert a time in milisecond into UTC date time

Your "milliseconds" value is obviously relative to a base date/time.

By subtracting the milliseconds from the known value it is supposed to represent, we can find that base value:

DateTime baseDate = new DateTime(2022, 9, 29, 13, 48, 0, 0, DateTimeKind.Utc).AddMilliseconds(-1664459293023);
// 31/12/1969 23:59:46

That seems like an odd choice, so I'm assuming you've simply missed out 13 seconds from your expected value. That would leave you with a base date of 1970-01-01T00:00:00Z, which is the Unix epoch[^].

You will need to use that value in your calculations:

private static readonly DateTime UnixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

public static DateTime ConvertMillisecondsToTime(long milliseconds)
{
    return UnixEpoch.AddMilliseconds(milliseconds);
}

That will give you:

DateTime DateUTCKin1 = ConvertMillisecondsToTime(TimeKin1);
// 2022-09-29T13:48:13Z

NB: If the milliseconds actually represent the "Unix time", then you could use the DateTimeOffset.FromUnixTimeMilliseconds[^] method instead, which would give you a DateTimeOffset value:

DateTimeOffset DateUTCKin1 = DateTimeOffset.FromUnixTimeMilliseconds(TimeKin1);
// 2022-09-29T13:48:13Z