Custom Header question

Hi,

My main buddypress website is using Corporate theme (ex. mywebsite.com) and I created a new blog called anotherblog.mywebsite.com. I used corporate theme also because I want same look and feel. I just intend to use the second blog for another function of the website.

I would like to know how I could access the headers.php of my anotherblog.website.com. It must be separate from my main website. Where can I find them? I want to modify the menu of my sub blog's header.php.

Pls. advise. Thanks!