If you have a will from a previous country then just re-write it yourself so it's for Hong Kong, outlining your partner and any major housing, etc.
Advantages
1. You don't need to go through a lawyer - And this is where people usually pay Big money to some lawyer for something that is effectively FREE.
2. You can change it at will.
Just need two witness's to certify it. And they can be anyone.
Point to note - if you're gone through a divorce or you have very complicated details that are delicate then by all means use a lawyer.