Hello I'm Nepal national, but now am living in japan for study

Buddha, the first thing is to prepare the relevant documents including copy of your passport, a recently-taken passport-style photo, proof of your financial support, flight itinerary, accommodation arrangement and your travel plan. Next, post the application to HK immigration department to apply for it. Below is the postal address:
Receipt and Despatch Sub-unit
HK Immigration Department
2/F, Immigration Tower
7 Gloucester Road
Wan Chai, HK