Display featured image in blog posts?

I can’t show the page that I need help with, because it’s on the Dashboard, but on a site that was done for me about 2 years ago, the blog posts show the featured image in the posts-page. It’s using the Enfold theme. I’ve created a new site, that uses Twenty Seventeen, but there’s no image shown. This is the Twenty Seventeen (https://postimg.cc/8J6p85fJ) and this is Enfold (https://postimg.cc/xNV092Ls). Could someone please tell me how I can have the featured image shown on the current site, like the old one?
Thank you!