add zero to cells with cells with less that 8 characters

[Kenneth Hobson]

Welcome to the forum! If data in A2 and down:

Sub cDates()
  Dim r As Range, c As Range
  Set r = Range("A2", Cells(Rows.Count, "A").End(xlUp))
  For Each c In r
    c.Value = DateSerial(Right(c, 4), Left(c, Len(c) - 6), Left(Right(c, 6), 2))
    c.NumberFormat = "mm/dd/yyyy"
  Next c
End Sub