Following is a recent mail from Thai Airways and the link worked as previous times:

Dear Valued Customers,

Thai Airways is pleased to inform you that our Royal Silk Class passengers may pre-select meals when traveling on International flights from Bangkok.

The Selection has to be made at least 72 hours before your flight via THAI Contact Center (662) 356 1111 or click

https://www.thaiairways.com/app/pre_...als/lang?id=EN