Hello,
Thank you for contacting us about changing the background image into a slider. The Background tab in the customizer allows you to change the background image and how it displays. There you can choose if you want the background image to be Fixed, Scroll, or use a Parallax effect (slides at a different rate than your content ).
If you want a slider gallery as the background image, there is no “built-in” way to accomplish this in BoldGrid. But, since BoldGrid is powered by WordPress there are several Background Slider plugins available for adding this functionality.
Keep in mind with any 3rd party plugin, you will have to test it to ensure it is compatible with your specific site.
Thank you,
John-Paul