You can customize the final message that will be displayed to your form users after they have filled and successfully submitted your form. This custom submission message overrides the default ‘Your response has been sent’ message. You can also add images, formatting, or include links in your custom submission message.
To add a custom submission message, navigate to your form Settings page then click on the Post Submission Page tab from the left navigation bar.
In the Post Submission options, there is a Submission Message option. Click the Set final message button to include your custom message in the pop-up editor, then click on the Save button to save your composed message.