I suspect you didn't find a solution on the internet because you looked simply for a solution and not the parts needed to build your own solution.
You mention you are a VBA beginner, please take the below answer to be of educational use and begin you in getting you where you need your tool to be. Note, if it doesn't answer your question because of information that was not included, it has still answered your question and the missing information should form part of a new question. That said, lets get this function up and running.
From what you have written I have interpreted the requirement to be: -
- Look over all worksheets in a workbook ('worksheets can be more than one in number')
- Check every column to see if it holds a date value
- If it does, set the whole column to a specific format
What is needed to accomplish this is iteration(loops), one to loop through all worksheet, and another to loop through all columns: -
The is pseudo code of the target: -
.For each Worksheet in the Workbook
..For each Column in the Worksheet
...If the Column contains dates then format it as required
..Process next column
.Process next Worksheet
We achieve this using a variable to reference a Worksheet and using a loop (For Each) to change the reference. The same goes for the columns.
Public Sub Sample()
Dim WkSht As Excel.Worksheet
Dim LngCols As Long
Dim LngCol As Long
'This loop will process the code inside it against every worksheet in this Workbook
For Each WkSht In ThisWorkbook.Worksheets
'Go to the top right of the worksheet and then come in, this finds the last used column
LngCols = WkSht.Range(WkSht.Cells(1, WkSht.Columns.Count).Address).End(xlToLeft).Column
'This loop will process the code inside it against every column in the worksheet
For LngCol = 1 To LngCols
'If the first cell contains a date then we should format the column
If IsDate(WkSht.Cells(2, LngCol)) Then
'Set right to the bottom of the sheet
WkSht.Range(WkSht.Cells(2, LngCol), WkSht.Cells(WkSht.Rows.Count, LngCol)).NumberFormat = "dd/mmm/yyyy"
End If
Next
Next
End Sub
Hopefully that has all made sense, this does work on the premise that the header row is always row 1 and there are no gaps in the columns, but these are separate issues you can approach when you're ready to.