HI @Lori
You can dive the date formats in the array of strings in the below expression.
DateTime.ParseExact(aa,{"yyyy-MM-dd","yyyy/MM/dd"},System.Globalization.CultureInfo.InvariantCulture,System.Globalization.DateTimeStyles.None).ToString("yyyy-MM-dd")
You just need to add the formats in the array if in case any other formats
Regards
Sudharsan