The comment form function which is defined in the framework-extender.php is an old function which is not using anymore..
Comment form function call is in file comments.php .
comment_form(array('title_reply' => __('Leave a Comment', 'mo_theme'), 'title_reply_to' => __('Leave a Comment to %s', 'mo_theme'), 'cancel_reply_link' => __('Cancel comment', 'mo_theme')));
You need to modify the function arguments to modify the default comment form .
More details are available here – https://codex.wordpress.org/Function_Reference/comment_form .
You can check this article –
https://www.inkthemes.com/how-to-easily-customize-wordpress-comment-form/