How to force custom background image instead of the featured image in Blowfish theme?

[Amakatus]

I'm a beginner at using the Blowfish theme for my Hugo website and I'm facing an issue where the featured image is always being used as the background image in my articles, even though I want to use a custom background image instead.

Here's what I've tried so far:

I modified hero.html in the layouts/partials/ folder to force the background image to be by setting background-image: url('mypath/toimage');.

I also checked https://blowfish.page/docs/thumbnails/

How can I make sure that my image is always used as the background and completely override the default behavior of using the featureimage? I think this is possible because in the demo-website it's working exactly how I want

Any help or advice would be greatly appreciated! Thanks in advance.