Stretch featured image

This is a duplicate on my previous forum and a moderator redirected me here.

I’m having trouble fixing my wordpress header image. I am using Goedemorgen theme.

basically, I want the modern look that has a full-width featured image like their demo:
https://demo.goedemorgenwp.com/default/

but when I try to change mine. It has these spaces and it’s just sitting at the center of my homepage and I find it really boring.
Like this: https://mmafn.000webhostapp.com/

Please help me fix this issue. I’m really new to developing wordpress sites and would like to learn alot. Thank you.

PS.
Also if you could give me some advice to add a button to the featured image just like on their demo website. Thank you!