Base on this article
If I want to change it back, is there any way I can do it besides creating new?
Because I have this template that I accidentally hit that button and there are almost 50 landing pages that uses this template, and not all are all good on this upgrade. So I need to change it back the way it is.
If you approved it, you can't revert it. But if it's still a draft then you can just discard it.
The good news, however, is that the button actually doesn't do much so it's probably not too difficult to get it back to what you want. They are listed in the document you referenced.
What is wrong with the template now that you want to revert it? You prob have a few options.