Thumbnail Image Question

Hello! I modified the posts_loop_template.php file to show the thumbnail in my list just fine. Wondering if there is a way to have it take the first image in the post (not assigned as featured image) and use that for the thumbnail? Reason being is that I am changed over to a theme that uses odd sized featured images and I don’t want to go back and manually reformat everything. (sela)

<!-- NOTE: If you need to make changes to this file, copy it to your current theme's main
	directory so your changes won't be overwritten when the plugin is upgraded. -->

<!-- Start of Post Wrap -->
<div class="post hentry ivycat-post">
	<!-- This is the output of the post TITLE -->
	<h2 class="entry-title"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>

	<!-- This is the output of the EXCERPT -->
	<div class="entry-summary">
		<?php the_excerpt(); ?>
	</div>

<!-- This will output of the featured image thumbnail  -->
	<div class="featured-image">
		<?php the_post_thumbnail( 'thumbnail' ); ?>
	</div>

	<!-- This is the output of the META information -->
	<div class="entry-utility">
		<?php if ( count( get_the_category() ) ) : ?>
			<span class="cat-links">
				<?php printf( __( '<span class="%1$s">Posted in</span> %2$s', 'sela' ), 'entry-utility-prep entry-utility-prep-cat-links', get_the_category_list( ', ' ) ); ?>
			</span>
			<span class="meta-sep">|</span>
		<?php endif; ?>
		<?php
			$tags_list = get_the_tag_list( '', ', ' );
			if ( $tags_list ):
		?>
			<span class="tag-links">
				<?php printf( __( '<span class="%1$s">Tagged</span> %2$s', 'sela' ), 'entry-utility-prep entry-utility-prep-tag-links', $tags_list ); ?>
			</span>
			<span class="meta-sep">|</span>
		<?php endif; ?>
		<span class="comments-link"><?php comments_popup_link( __( 'Leave a comment', 'sela' ), __( '1 Comment', 'sela' ), __( '% Comments', 'sela' ) ); ?></span>
		<?php edit_post_link( __( 'Edit', 'sela' ), '<span class="meta-sep">|</span> <span class="edit-link">', '</span>' ); ?>
	</div>
</div>
<!-- // End of Post Wrap -->

https://ww.wp.xz.cn/plugins/posts-in-page/