Hello @frannyo ,
You can contact to theme support about the requirement or hire an expert to do this.
Alternatively if are about code then follow and implement this flow.
You have to create some options with exiting setting.
1) Make a checkbox for selection ( video slide or image slide)
2) Create an option to input video url ( mp4 video less than 20MB )
3) Call above points in exiting code and use video url in html5 video tag.