Originally Posted by
tearex
Edit: misread
Might also be worth asking in KLM forum, but I would think they should allow you to change your second leg without issue at least.
It is a KLM stock, so KLM should have ability to accommodate the poster on their own metals - the issue is, KLM did not sell the ticket directly so the "ownership" sits with the OTA. Some airlines are willing to take "ownership", often with a fee, then the tickets become under control of the airline, and can be more flexible to accommodate schedule changes. NOT all airlines, especially an international airline would accommodate on tickets not issued directly by them.
If the tickets not issued by the operating airline, then there would be absolute no change. Had this happened with QF on a BA issued ticket on QF flight, not even co-share just last month. Cannot even pay to get it changed.