If you book an award on Thai Airways using another carrier’s miles, you probably won’t get a seat assignment at first. Luckily, it’s quite easy to get your record locator and an advance seat assignment.
You can call the Thai Airways office in LA at 1-800-426-5204, or even better, you can email them at email@example.com. Just be sure to include your ticket number, name, schedule, and seat preference, and they should be able to take care of everything for you. And once you have your record locator, you can use the Thai Airways website to pre-order a meal if you’re traveling internationally in Royal First or Royal Silk classes.
Be aware that this only works for non-domestic itineraries on Thai, as seat assignment only occurs at check-in for those domestic itineraries.