First, you’ll need to create a custom field. A plugin like this is great for that: https://wordpress.org/plugins/advanced-custom-fields/
Then, you’d add your video HTML to the custom field.
Lastly, you need to add this function, and change the custom field to the name you chose when you create your own custom field: https://wpshowposts.com/support/topic/wpsp-with-videos/#post-10661
Hope this helps 🙂