So there’s a few way’s to do this but I feel the easiest way;
Create a popup that has all the same exact inputs has the original form and all it does is just copy what’s in the previous inputs. When the user selects Submit, have the button trigger the popup and it will display everything they just entered on the popup screen that can say Verify info or what have you, and a confirm button that will then save to the data file. A cancel button that simply closes the popup and returns to the form and they can change whatever they need.
Or you could simply add a popup that just says are you sure this info is correct? with a Confirm or Cancel button, cancel would close the popup and they can verify or Confirm would save it.