Any idea how I can modify the theme to automatically insert the featured image in the post where it belongs?
Sure! If you’d like to add a featured image to the single post view, you’d make a copy of content-single.php and place it in the child theme.
If you haven’t already made any changes in this file in your child theme, you’ll see this code on line 31:
<div class="entry-content">
Right after that line, you can add the featured image with some code like this:
<?php
if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
the_post_thumbnail('medium', array('class' => 'alignleft'));
}
?>
You can choose another size instead of medium – it’ll follow the dimensions you’ve set for each size under Settings > Media. The class “alignleft” will align the image to the left of your post. You can change it to “alignright” if you prefer, or add a custom class that you apply CSS to in your child theme’s stylesheet.
Function reference: https://codex.www.ads-software.com/Function_Reference/the_post_thumbnail