This requires unmerging the cells to do. Try this. (and thanks for
asking). I need this for something else I do and never even thought about it.
Sub test()
Dim r As Range
Dim myRange As Range
For Each r In ActiveSheet.UsedRange
If r.MergeArea.Count > 1 Then
Set myRange = r.MergeArea
r.UnMerge
myRange.Value = r.Value
End If
Next r
If you truly merged the columns, you lost the data in all but the left hand
column so there is nothing unmerge.
If you mean you combined the columns data using the CONCTENATE function or
the ampersand like +A1 & B1 & C1 then I would suggest trying Data>Text to
Columns to undo the combining after you copy/paste special/values.