To add multiple classes to the Contact Form 7 Submit button, you can follow these steps:

1. In the WordPress dashboard, go to Contact > Contact Forms and select the form you want to edit.
2. In the form editor, find the Submit button code block. It should look like this:[submit "Send"]
3. To add multiple classes, modify the code like this:[submit class:btn class:btn-primary "Send"] or [submit class:"class1 class2" "Send"] 

   In the above example, “class1” and “class2” are the classes you want to add. You can add as many classes as you need, separating them with a space.

4. Save the changes to the form.

That’s it! The Submit button should now have the additional classes you specified. You can use these classes to style the button using CSS.