Change post showing in custom feed

I am working with a client that needs to change the blog feed showing up on their homepage. Their site is built with WordPress by another company and they currently have a feed on the homepage that shows the latest post automatically. I need to change this to show 1 post from their new blog which is hosted on blogger. This is the code I’m seeing on the custom homepage php file, but I do not know enough about PHP to edit it. My instinct is to remove
<?php echo BLOG_URL ?>

and replace it with the URL to the new blog, but I also don’t think that is the only thing I should edit. I appreciate any assistance.

<?php $query = new WP_Query("cat=-4"); if(!$query->have_posts()) echo "Couldn't find posts"; else $query->the_post() ?>
        <strong class="title">FROM THE BLOG</strong>
        <?php the_excerpt() ?>
        <a href="<?php echo BLOG_URL ?>" class="more">READ MORE</a>