How to convert exported text date to desired date format with excel vba.

Maybe:

Sub sktneer()
Dim cell As Range
Application.ScreenUpdating = False
For Each cell In Range("A1:A" & ActiveSheet.UsedRange.Rows.count + 1)
    cell.Value = Left(cell, 4) & "/" & Mid(cell, 5, 2) & "/" & Right(cell, 2)
    cell.NumberFormat = "yyyy/mm/dd;@"
Next cell
Application.ScreenUpdating = True
End Sub