VBA / Find Column Header And Reformat (date) Values In Columns

I have VBA code to perform some actions on data in excel file and then convert all that data into semi-colon separated CSV/text file (code below).

Now, all I want is to add VBA code in the existing macro to find a column header (say, "Application date") and then convert all the dates into YYYY-MM-DD format. The original values in this column don't have a fixed date format.

Code:
Public Sub ExportToCsvFile(FName As String, _
Sep As String, SelectionOnly As Boolean, _
AppendDataOnExistingFile As Boolean)
Dim WholeLine As String Dim FNum As Integer
Dim RowNdx As Long Dim ColNdx As Integer

[code]....