Selecting multiple columns for reformatting

I need a quicker and more efficient way of reformatting date columns. I put together the following code but it only allows me to specify a single column or continuous range.

I would like to be able to quickly identify multiple columns that need to be reformatted.

I would like to be able to input the column letters (a,b,d,e,f ect…) and have each of the respective columns selected for reformatting.

Any ideas on how do to this would be greatly appreciated.
Thanks!

Sub DateFormat()

Dim ActSheet As Worksheet
Dim clm
Dim frmt
    Set ActSheet = ActiveSheet
    clm = InputBox("What Column Do You Need to Reformat?", "Column Selection", "a")
    frmt = InputBox("Format?", "Format", "dd/mm/yy hhss")

    If clm = "<>""" Then
    ElseIf clm = "" Then
        MsgBox "Form was null.  Select range and try again"
    End If
    
    On Error GoTo Etrap
    
    Columns(clm).Select
        With Selection
        .NumberFormat = frmt
        End With

Etrap:
    Beep

End Sub