Insert Final Submission Slide into Assessment Prior to Results Slide

In a Storyline assessment that uses question banks from which half of the questions are drawn at random, I would like to display a final submission slide after completing the last question from the last bank or a caption upon reaching the last question. The final submission slide or caption will advise the learner that this is their last chance to review and change their answers before final submission using the previous and next buttons. In the scene, I have the slide between the last question bank and the results slide. On the LMS, it will not let me change answers when I navigate back from the final submission slide. This may be because all answers have been submitted. Is there a variable and/or trigger that can display a slide or caption advising learners that they are on the last question and enable them to go back and change their answers prior to final submission?