In my case I don't have a "prev" button, so I didn't do anything specific to make that happen, but yeah that's definitely something you have to take into account if you want a "prev" button.
For now I have a "reset" button with a very simple script to manually set the slider to 0 whenever I want, while I'm still figuring out how to add more stuff. I don't know yet how I'm gonna replace that in the final project! :p