You can set up background slider by option panel. When you will select dropdown. you need to select static Background Slideshow. Then select of no. slider show. you can select No. of the slider. Now you can upload images in slideshow step by step.
Go to => Webriti Coming Soon Pro => Customizer => Background Settings
- Select Background -> Select Background Slideshow.
- No. Of Slide-show -> Select number of slide for background slider.