Do you mean an anchor to the form on the bottom of the page, like this one (I mean, the one I’m typing in right now to reply to you and that you will use if you reply to me 🙂 ).
If that’s it, then add in an anchor to form-reply.php* after the new reply div, like so:
<div id="new-reply-<?php bbp_topic_id(); ?>" class="bbp-reply-form">
<a id="the-reply-form"></a>
If that’s not it, then if you post a link, I’ll tell you which template it’s on – there’s form-topic.php as well – that one’s for topics.
*this should be in a child bbpress theme – instructions are here: https://codex.bbpress.org/theme-compatibility/ — apols if you already know this, am adding for completeness!
