To create a custom opt-out or confirmation page and redirect it to an external site, take these steps.

1. Go to Landing Pages and click the landing page name.
2. Click the Manage Site
3. Expand the name of the web form and click Form.
4. Click the form in the right pane.
5. Expand the Object Properties
6. Select Submit to edit properties.
7. In the Object Properties pane, go to Actions and then go to Take user to URL:
8. Enter a fully formed URL of the custom page where you want the user who submits the form to be taken.
9. Click Save & Close.