Hello Nam,
I'm a little confused when you say you want to make a reservation with a specific reservation number.
Airbnb gives a reservation number only after a reservation is made.
Usually you make a reservation by logging on to the website, finding the listing you want and then clicking on "Request to book" or "Book". You can also do this with the Airbnb phone app.
If you're having trouble you may want to contact Airbnb support.
Type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. Scroll down a little in the list of suggestions that appears and click on the "Contact Airbnb: A Community Help Guide[UPDATED]" one. That lists phone numbers and ways to contact them via Twitter or Facebook.
Steve.