Change the comment author name on hestia

Hello,

Ive using using the hestia theme for a while now. Im pretty impressed so far.
I want to change the displayed comments author name, somehow this is always the full name of the user. I couldnt find settings for that so i tried to add a filter in my functions.php of my child-theme:

add_filter('get_comment_author', 'my_comment_author', 10, 2);

function my_comment_author( $author = '' ) {
    // Get the comment ID from WP_Query

    $comment = get_comment( $comment_ID );

	if (!empty($comment->user_id)){
		$user=get_userdata($comment->user_id);
		$author=$user->display_name; // this is the actual line you want to change
	} else {
		$author = __('Anonymous');
	}

    return $author;
};

But even if I just return some string, the displayed comment author name wont change.

Best regards
Simon

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