I believe that if you stay airside (i.e. do not pass through HK immigration then you do not need a visa.
However if you have any checked bags then I do not believe that Myanmar national ariline will check them through to HK Express. So you would need to enter HK in order to collect your bags and check them in again for the onward flight. To do this you would need a visa. The normal time to get a visa is 4-6 weeks, so it is probably too late for you to get a visa now.
So basically you can only make your journey if you travel with cabin baggage only.
Thank you for information and advice
https:/…visit-visa-entry-permit.html indeed confirms no need for visa if just transiting (i.e. staying airside) but to claim luggage and check in again (note: T2 is not a real terminal, it's a check-in desk area only) you do need visa to clear immigration and claim your luggage.
As it's in three weeks, you don't have the time to apply for visa, so no choice but to fly with hand luggage only.