Procedure:
You can use the SharePoint Designer to achieve it.
- Create a new page named as “Thankyou.aspx” page under the Site Pages.
- Open the site in SharePoint Designer 2013, click Lists and Libraries, go to "Forms" section. Create a New Form by clicking on "New Item Form"
- Give it a Name, choose form type as "New Item Form" and enable "Set as default form for the selected type" and click on "Ok" to create the new form.
- Edit the New form we've just created. Open the "New.aspx" page with Advanced Mode in SharePoint Designer.
- Search for the savebutton1,savebutton2, delete all two “Finish” buttons.
- Insert SharePoint Form Action button from "Insert Menu >> SharePoint >> Form Action Button"
- Select the Form Actions "Commit" and "Navigate to Page" .
- Select the “Navigate to page” action, click “settings” to set the target page ,and click "OK".
- Rename the Form Action as Finish.
- Save and close the page.
You can also refer to the following article, although it is for SharePoint 2010, it also fits for SharePoint 2013.