The Hero section’s background shape is specified and defined for individual styles that you can choose from the Background Style dropdown. That’s mean the background shapes are fixed for individual Hero styles.

But there are scopes to change the background shapes yourself. You can find all the background shape image in the Saasland Core plugin. Go to saasland-core/widgets/images folder and replace your targeted shape image with your own shape image. 

Note: Inspect with your browser developer tools to find the image locations with the name.