How to Create Description for RSS Feed

Hi, I saw a few options in the code library for RSS, but none that mentioned how to add a description for RSS feeds. Right now my RSS feeds have a description being pulled in but it shows very unhelpful text (eg this post was published….) and I don’t know how to change it since I don’t know where it’s actually pulled in from.

Is there a snippet to both add a description that will replace the old one and hopefully if it can change the length of text that would be a bonus!

I saw this one snippet online on another site but it’s returning errors:

function insertInfo($content) {
$content = $content.’This text will display within your rss feed’;
return $content;
}
add_filter(‘the_excerpt_rss’, ‘insertInfo’);

thanks