If you are just using a common redirected thank you page, you can handle this by going to Seller Admin>Edit Account Preferences. On that page, delete the URL in the Common Thank You Page URL field and then click Submit.
If you are using product specific redirection then you will want to go to Seller Admin>View/Edit/Delete Products, select the product and click Edit. On the page that comes up remove the check mark for Redirection and then click Next until you can Submit the changes.
