C# Converting YYYY-MM-DD to MM/DD/YYYY ("-" TO "/")

Hey I have been having trouble with something.

string record = el.InnerText;
var result1 = parseString(record);
var StartDate = string.Join("", result1.ConvertAll(r => string.Format("{0}", r)).ToArray());
//DateTime strStartDate = DateTime.ParseExact(StartDate, "mm-dd-yyyy", CultureInfo.InvariantCulture);
var EndDate = string.Join("", result1.ConvertAll(r => string.Format("{1}", r)).ToArray());
//DateTime strEndDate = DateTime.ParseExact(EndDate, "mm-dd-yyyy", CultureInfo.InvariantCulture);

This is the parseString function:

private static List<string[]> parseString(string input)
    {
        var pattern = @"Start\s+Date:\s+([0-9-]+)\s+End\s+Date:\s+([0-9-]+)\s+(?:Warranty\s+Type:\s+\w+\s+)?Status:\s+(\w+)\s*";
        return Regex.Matches(input, pattern).Cast<Match>().ToList().ConvertAll(m => new string[] { m.Groups[1].Value, m.Groups[2].Value, m.Groups[3].Value });
    }

The DateTimes aren't working because I am guessing that "-" is not a valid character when converting a string to DateTime.

I tried record = record.Replace("-", "/") but that ended up messing up my string and it stopped showing up (from html page).