How can I implement a back request at the submit (end) page

I have following case. Some body will add appointments to my system. I must check if in the database is a appointment.(via php)
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If a conflicting appointment was found. I woud like to ask the user if he is sure to add the appointment nevertheless of the conflict.
How I must implente this functiunality?
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If i use a normal submit button i will referd to start page (without data).
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Other vice how can I add a page beetween start_page and end_page?

Hi Collie,
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add new page using the page icon in the Page Group toolbar then drag the new page above the end_page, or just use the new page as an end page and rename the end_page to middle!