Visa office in HK?

Hello! I plan on traveling to HK next week to visit for the first time ! I have also been granted permission with the appropriate paperwork to change my Chinese marriage entry permit to a work Z type there in HK. Where is the office in HK located for this? ....I haven't an address for the relevant offices there ? And since I plan on staying the week, can you tell me how much it costs? And how long would it take to get for an American citizen? Also on arrival when I get to HK should I have some paperwork with me in order to apply for HK entry ?

Thanks in advance !