Hi Karen!
Currently, the "Previous Slide" trigger goes back to the Previously Visited slide - it doesn't work quite like a back button.
We have a current feature request to allow users to set logic for the Previous slide trigger. I will link you to the feature request, and we can update you with any news.
In the meantime, you can create a specific trigger to 'Jump to Slide X when user clicks the 'Prev' button, and then slide x would be shown.
If you are using the 'Jump to slide' - 'Previous' slide when user clicks 'Prev' button, then you would go to the slide previously viewed (like a browser back button).
I hope that helps! Please let me know if you need additional assistance.