Reply To: Modify forum index page and some

Place something like this in content-forum-archive.php if you copied it into your child theme to display the login form above the forum archive. You can also place it above single forums by adding this exact code into content-single-forum.php and for topics in content-single-topic.php.

<?php if ( !is_user_logged_in() ) : ?>

    <div class="bbp-forum-login-form">
        <?php echo do_shortcode("[bbp-login]"); ?>
    </div>

<?php endif; ?>