How to replace default page created in facebook with page created with static html application?

Question

Facebook

I'm trying to make my facebook page. I'm using the "Static HTML: iframe tabs" application to create the original page. Made a page using this application. But I can't replace the default page with the page created in this app. There is no "Main Tab" option in the "Privilege Management" page settings. And in all instructions there is a link to this option.
How to change the default page to the page made in "Static HTML: iframe tabs" app?
And why is the "Main Tab" option not available?

Answer 1

It seems that they removed it when switching to a new design.