Anyone know how to add videos to a multirow section so that I can choose between image or video
You can tweak the multirow section to support video by adjusting the schema so it accepts a video setting instead of just images. That way you can switch between the two. The harder part is making sure it plays smoothly without breaking the layout.
Have you looked into whether your theme actually allows adding a video input type in the section schema?
my theme is dawn theme
The multirow part of most Shopify themes only supports images out of the box. You have to edit the Liquid file of the section (sections/multirow.liquid or whatever it is called) to add the videos. When a video is selected, render <video> instead of <img> on a condition with new setting for video_url (or video_upload) in the schema.