This filter can be used for adding new classes to the div with the .wpd-comment-left class. The hook works only for the #1 and #3 layouts.
Changelog
Since 7.0.0 version
Parameters
$class (type: string) – the class that should be added to the div with .wpd-comment-left class
Usage
add_filter("wpdiscuz_comment_left_class", function ($class) {
$class .= " my-custom-left-class";
return $class;
});