By default in blog posts, you should set featured images and banner images. But if you want to use the featured image as a banner background you can simply make the following changes.

Activate the Child Youplay theme and copy a single.php file to it from the parent theme. Then you can make customizations in this file.

Open single.php and find this line:

echo do_shortcode('[yp_banner img_src="' . yp_opts('single_post_banner_image', true) . '" img_size="1400x600" banner_size="' . yp_opts('single_post_banner_size', true) . '" parallax="' . yp_opts('single_post_banner_parallax', true) . '" top_position="true"]' . ($banner_cont?wp_kses_post($banner_cont):'<h1 class="h2">' . get_the_title() . '</h1>') . '[/yp_banner]')

Change it to this one:

echo do_shortcode('[yp_banner img_src="' . get_post_thumbnail_id() . '" img_size="1400x600" banner_size="' . yp_opts('single_post_banner_size', true) . '" parallax="' . yp_opts('single_post_banner_parallax', true) . '" top_position="true"]' . ($banner_cont?wp_kses_post($banner_cont):'<h1 class="h2">' . get_the_title() . '</h1>') . '[/yp_banner]')