bbPress templates can’t be selected from the admin as they can, for instance, for a WP page. bbPress looks for the following template files in your *main* WP theme directory in the following order:
1. bbpress.php
2. forum.php
3. page.php
4. single.php
5. index.php
Most themes are going to have page.php by default so it’s likely that bbPress is pulling that as the forums page template. Copying and renaming that to bbpress.php or forum.php will allow you to customize a forum-only page template. NOTE: this is the containing page template (just like for WP pages) and is *not* where you will edit the forum files themselves.
