The simplest way, I should think, would be to go to that module and put an "Exit Sub" statement immediately after the Sub statement. That way you keep the code (in case you want to refer to it later), but it doesn't do anything.

Another way would be to remove the module entirely; you can "export" it at the same time, so you'll have the code around if you need it again.

You could, of course, change your security settings so that Excel refuses to run the autorun macro without your permission. But I don't think you can make that setting specific to one workbook, so Excel would ask you about macros on every .xlsm, every time you opened one, so maybe that doesn't appeal to you.