How do I edit the thank you page?

You can edit the Thank You Page shown after the form is  submitted, you could change its content and even redirect your users to an external page. 

Please check this following guide in order to get more details about it: https://www.jotform.com/help/211-Setting-up-the-Thank-You-Page 

Let us know if you have any question, we will be glad to help you. 

Please go through this detailed guide :

https://www.jotform.com/help/211-Setting-up-the-Thank-You-Page

you can also set up your custom created thank you page.

Hope this helps!