If you need the Thank You message to open a new window to a certain URL, please head to Components >> RSForm!Pro >> Manage Forms >> edit your form >> Properties >> From Info, edit the Thank You message in HTML mode and place the following script:
in the Thank You message's text.
You might encounter issues in saving the script when editing the Thank You message in HTML mode. This is not being generated by RSForm!Pro, but by your editor, as it might be stripping HTML tags for security reasons. To fix this, please disable the editor from Site >> Global Configuration >> Site >> select 'Editor - none' in the 'Default Editor' drop-down.
After adding the script in the Thank You message, you can re-enable the editor.