I was in the exact same situation. I called Reservation and they fixed it for me (based on a condition that my ticket allows changes of the original departure city in China). They had to charge me a ticket reissue fee under the same booking reference number for the service. It was 33USD (1000TWD) in my memory.

However i don't know what if your tix rule doesn't allow such changes. I hope you could or they could find ways around it.

Good luck.