I booked a flight from singapore to Lisbon in business via Rome. Initially I was going to meet someone for lunch in Rome, so after landing at 8am, I selected the flight out at 4pm.

But lunch is no longer an option and I was looking to change my flight to the earlier c connection at 12. But TAP and Singapore won't let me, saying I need to contact the OTA. And the OTA is trying to re- price the whole flight at a significant cost which isn't worth it.

I wanted to see if anyone has any experience of being able to change this flight mid way through, in Rome, to an earlier one on the day? Singapore I presume won't be able to do it, so I'll have to try it in Rome? After the first leg starts, I presume it'll be down to TAP and not the OTA?