Hi There,
Thanks for writing in.
We’d love to help you with this however the customization is beyond the scope of our support. It would be best to contact a developer to this customization. I could only share some of my analysis of the customization.
As I checked the code or the slider in the link. Upon hovering the image, there is a class added to the text that is removed from the previous text so that the background of the recent hovered will be shown.
Possibly the customization used is script removing and adding class when hovered and CSS for the background images changed when the added class is enabled upon hovering.
Hope it helps.
Let us know how it goes.
Thanks.