Customised Function

=TEXT(A1, "YYYY-MM-DD")

Function ColumnLetter(ColumnNumber As Long) As String
    Dim N As Long
    Dim c As Byte
    Dim s As String

    N = ColumnNumber
    Do
        c = ((N - 1) Mod 26)
        s = Chr(c + 65) & s
        N = (N - c) \ 26
    Loop While N > 0
    ColumnLetter = s
End Function