Slider featured image issue

I am new to wordpress and have installed a pre made theme from Blue Gel Media; eveything seems to be working and I’m slowily figuring out how to propagate my own content into the site. The theme has a slider and a carousel.
When I updated the feature image in the Carousel it worked fine and up came the image on my page. However when I try to set a feature image for the slider it does not work. Do I need to do more for the slider than simply click on “feature image”? I am trying to replace their placeholder imagery with my own

Thanks
Glenn