Only subscriber role user can comment not other

I suggest adding a snippet to the theme file where the comments form is loaded that checks to make sure there is a logged in user and then, if that user a Subscriber, then show the comments form to them. The examples below use the Twenty Sixteen theme:

In comments.php:

// First, get the current user and check their role
$user = wp_get_current_user();
if ( in_array( 'subscriber', (array) $user->roles ) ) {
    // The current user has the subscriber role, show the form
    comment_form( array(
        'title_reply_before' => '<h2 id="reply-title" class="comment-reply-title">',
        'title_reply_after'  => '</h2>',
    ) );
}

This way, only those users with the subscriber role will see the comments form.