Cannot change the backgound in slider

Hi there,

I just purchased Woodmart and downloaded a cosmetic theme. Now I would like to change the background of the slider, but cannot do it with Elementor Pro. How do I change it? I tried to change it in “slides” – “slider” – “edit” – “featured image” – “update” but it did not change the image to the one I chose from the gallery. How do I change it please? Thank you