Hello PaulDJ8& 

You may upload your image to the Studio->Storage->Images area. Then take the URL of the uploaded pic (it will look like [UNA URL]/s/sys_images/ze3dw7y2eyianurmrxkcbiqvvvqdjc9q.jpg ) then paste this URL instead of Splash like <bx_image_url:spl-image-main.svg />