You need to create the pages in Adobe InDesign.
Duplicate the pages you have already done and move them to after the pages you have already made.
Then reverse the order of the pages (that's if you've used pages - if you've one oversized page with margins then reverse your margins, all this is done manually)
You then communicate this to your printers, and supply a mockup of what you want if that's an option, if it's not an option, then I suggest you send a digital mockup displaying how you want the pages to be imposed.
Any of that make sense?
The best way to visualise this is to draw out a mockup using pen and paper and a rule.
Measure your page and the folds (even to scale if you haven't got paper large enough)
You'll see exactly how your pages should look when you view them on screen compared to your mockup you've created.
This will show you exactly where all the elements go, and the margins and how they should look etc.
Fold-out pages are sometimes called "island spreads" around here. The thing to remember about them is that each flap that folds out also has two sides, so you need to add its reverse on the opposite edge to either the previous spread (if it folds from the left page) or the next spread (if it folds from the right). Do that and it should be obvious where you can add content that will be seen.
Also worth nothing that some printers prefer to receive the "fold out/island spreads" as separate files. You can just leave placeholders in your document.
It's most likely you're island spread will be printed separately and colated back into the job later.
Check with your printers though - some are fussy and others are not - some have one way - and others have another way.