New Form Layout: How can I edit my thank you page?

As a matter of fact, I came to finding this page because the option to set up and customise the 'thank you page' seem to have gone completely, and I can't even find a comment about that.

I have checked your account and noticed you're using the "new forms layout". To edit the thank you page or redirect your users to a different page, you will need to scroll at the very bottom of the form builder, there you will find option to edit the thank you page: 

I hope this helps.