I am from Bangladesh, working in Oman MOH. Going to hongkong in August for 3 days.

Manisha, you go to HK for tourism purpose, right? If yes, you need to apply for a tourist entry permit.
Firstly, you need to prepare the relevant materials including copy of your passport, the application form, a passport-style photo, proof of your financial support, transportation arrangement, hotel reservation, your travel itinerary and your residence permit in Oman.
Next, submit the application to the embassy of PRC to apply for it.