Bob,
You may want to try this guide:
https://codex.bbpress.org/legacy/step-by-step-guide-to-creating-a-custom-bbpress-theme/
You will copy file and move them inside your existing theme directory. This will override the default theme that lives inside the plugins directory.
Good luck!
Luke
This was the previously mentioned link with “legacy” in it: https://codex.bbpress.org/legacy/themes-and-templating/ – this references a templates directory which I believe has been taken out of the plugin architecture.
