Unable to change blog post preview image on main blog page

I have been building a very simple WP site for my wife, using the Gutenbiz plug-in, which has some very good features. Have run into a wall on one thing however. On her main blog page, which shows the various blogs she has created so far, the format includes what appears to be an image stand-in (grey and white rectangle, has shape of mountain and sun in it, simple graphic, see link) which her “author” image floats above, then below that is post title and short excerpt. I can access everything to edit the appearance using the “Customize” icon top of page, which opens up the Gutenbiz tools, on the left side of page. Except that image. Nothing in there, and I have tried turning on and off all the available items, including category, inner banner etc., allows me to either remove that image, or put the same image into that placeholder, using the image featured on the actual post. I tried editing the post the same way, and also the main post page in the WP dashboard, although there is little available there. Really at wit’s end on this one, seems like a global setting but cannot find it. Any advice on how to find the control for that image would be appreciated. Thank you, Dan

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