Upvote:1
Your original plan was for a stopover in Hong Kong, which changed when the pre-arrival registration failed; you cancelled the Singapore-Hong Kong ticket.
Connecting to the separately-ticketed Hong Kong/Kolkata flight may work, if you're allowed to board the Singapore/Hong Kong flight based on the onward AirAsia ticket. If it does, you could transit airside if you have a boarding pass for your next flight. AirAsia lets you check in online and print a boarding pass. Otherwise, it's located in Terminal 2; it does not have transfer desk at HKG.
With the revised itinerary, a fresh Pre-arrival Registration may be wise so that there is less risk of complications.