Removing the featured image from “blog-single-inner”

Hi!

I am now slowly moving into your Shapebox theme, but there is none thing I cannot handle myself – I do not use featured images in my posts, which makes all my posts look bad https://imgur.com/C33RjOV

Is there a way to change it, so I will just have a plain tile?
Or, as a future suggestion – a toggleable option to use the first image of the post as a featured image if there is none?

Thank you, or anyone, in advance!