asia miles redemption availability inconsistent between website and agent.

asia miles redemption availability inconsistent between website and agent.
All.
I used Asiamiles to book an award ticket for the below itinerary.
MNL DOH QR0933 06-Jun 18:35 22:50
DOH CPH QR0163 07-Jun 15:35 21:05
CPH DOH QR0164 11-Jun 22:35 5:50
DOH MNL QR0928 12-Jun 7:40 22:15

Now, I saw a flight available on KVS and also Asiamiles.com for MNL-DOH-CPH.
MNL DOH QR0933 06-Jun 18:35 22:50
DOH CPH QR0159 07-Jun 8:00 13:30



When I call Asiamiles for the change, they can not find this itinerary available.
I asked if I cancel MNL-DOH-CPH, and I will try to book that part online, the agent said it is OK, I need to pay $100 reissue fee, plus tax for 2000+ HKD.
However, when I booked the round trip, the tax was only HKD 468 for all round trip.

So questions.
1, what is the most easiest way to change the itinerary to QR933-QR159 since it is NOT available for agent?
2. Does anyone know what happens to the tax?

Thank you