Your BLAB page already has a main video option, which is viewed at the top of your main page.
If you would like to add different video to your product or service, perhaps highlighting that particular product or a video testimonial of a happy client of yours after receiving said product, you can do so by following the step below.
Open your Product/Service settings
Click on Cover Media at the top of the screen
Then scroll down
You will see option to Add YouTube Video.
If you want the video to apply to this specific product and not to ALL your products make sure to un-check the Global checkbox
Make sure to Save Changes by clicking on the blue button the top right of your screen.