Please, try the next way. You can use it for any header, only adapting the used constant:
Sub Excel_Format()
Dim ws As Worksheet, RngH As Range
Const myColName As String = "ColumnX" 'your column header
Set ws = ActiveSheet 'use here your necessary sheet
Set RngH = ws.rows(1).Find(myColName)
If Not RngH Is Nothing Then
With RngH.EntireColumn
.NumberFormat = "0"
.AutoFit
End With
Else
MsgBox myColName & " could not be found in the sheet first row..."
End If
End Sub
The header should exist in the first sheet row. If not, you should adapt ws.rows(1).Find(
writing the necessary row, instead of `...
Selecting, activating in such a context only consumes Excel resources, not bringing any benefit.