If they hold the flight for you, you will be met at the gate and escorted. If CX have rebooked you, you may be met at the gate and provided with new BPs.
If you are not met at the gate at HKG, then go to the transfer desk (you're going to have to go through transit security in order to get up to departures, anyway, and the transfer desks are right there. CX has priority queues at transfer desks.).
Once you're rebooked on CX you can deal with Air Asia for the CGK DPS portion.