Use Excel to Modify Access Table?

Sub Update_mdb_Files()

  Const strFILE_PATH As String = "M:\DataFiles" 'SET THIS FOR YOUR DIRECTORY
  
  Dim strDB_Name As String

  strDB_Name = Dir(strFILE_PATH & Application.PathSeparator & "*.mdb")
  Do While Not strDB_Name Like vbNullString
    Call Update_Table_ABC(strFILE_PATH & Application.PathSeparator & strDB_Name)
    strDB_Name = Dir()
  Loop

End Sub

Sub Update_Table_ABC(ByVal strDB_FullName As String)

  Dim objConn As Object

  Set objConn = CreateObject("ADODB.Connection")
  With objConn
    .Open "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & strDB_FullName & ";"
    .Execute "UPDATE ABC SET ABC.XYZ = 0 WHERE ABC.XYZ Is Null"
    .Close
  End With
  Set objConn = Nothing

End Sub