Mark,
You could really do this two different ways, but both will take a bit of programming.
You could use some client side to hide the submit button and add your own, so when the user submitted the form initially you display a summary field (you could do this also with server side code by creating a new page with the same form items but turn it to read only), then when you show the summary screen re-display the final submit button.
To do this the more supportable Kentico way, you can access the BizForm Global Events from your code behind and work with the On Before Save event handlers to create your summary form and then complete the final submit after confirmation of the information.
Here is a good place to start with the Kentico way: https://docs.kentico.com/display/K8/Working+with+form+data+using+the+API