you would have to edit and copy files from one to the other.
since its bbpress its mostly going to require copying the template files and bbpress.css , but i am not sure if your going to going to need a function for bbpress in the function.php in the theme or many more codes.
This could be really risky if you dont know what you are doing.
I recommend working on a local development area. WAMP for Windows , MAMP for Mac , LAMP for linux , and XAMP for all.
Help on this is really minimal on my side. Its more something you have to do yourself.
But if you do need help transferring i might come up with something.
Other than that it might be an answer of i dont have the time to this kind of thing right now.