Is there any way to add a class to .entry-content?

hello.

I want to add a class called daum-wm-content to the default entry-content class of the post.

<div class="entry-content daum-wm-content">

I tried adding some code as follows, but nothing works.

function add_daum_wm_content_class($content) {
 // extend entry-content class to daum-wm-content class
 $content = str_replace('class="entry-content"', 'class="entry-content daum-wm-content"', $content);
 return $content;
}

// Use filter to apply to post content
add_filter('the_content', 'add_daum_wm_content_class');

Could you please let me know if there is a way to solve this problem?

thank you.