I installed the latest bbPress. Everything went well. Then I decided to be an idiot and changed the bbPress url in the options page to my main site because when I clicked on my site name I wanted it to redirect back to my main site (the site name beside the bbPress logo).
I tried to re-install bbPress but it wont go past after installing bb-config.php
In the database, the value is stored in the bb_topicmeta table. A record that has a meta_key of uri holds the value, I think. That is record #3 in my fresh installation. It might be different in yours. Just find the key of uri and the value is the one you want, I think.