in February 2009 I booked an AONE3 ex ICN, commencing in September, and have flown the first 3 sectors. I am now in the UK.

The booking was through a TA in Seoul and the originating carrier was CX (ICN to HKG).

All remaining unflown sectors are on dummy dates as the travel dates I wanted were more than 360 days out from the booking date. The first of the next sectors is on BA

To change the dates from now on, am I best to do this through the TA who handled the booking, CX as the originating carrier or BA as the next carrier?