If you have the nerve to do it, you leave it as it is for now. If nothing happens until the day of traveling, you show up at the origin for check-in with TG. Either ground staff at origin will rebook the OZ flight, or you travel to BKK with TG and let OZ ground staff deal with the onward flight to ICN.

Under no circumstance you should accept the suggestion to contact the issuer of the ticket for rebooking (no doubt TG staff and probably also OZ ground staff will try this the moment they realise that this is an LH M/M award ticket). OZ can solve this at BKK as OZ rescheduled the flight and made the BKK connection impossible so just travel to BKK on the ticket as it is and let OZ deal with there.