Train arrival require swab?

Does anyone have any good intell on what is required (and what is actually transpiring) of/to travelers arriving to CM via train from a red zone, other than the "quarantine" and app usage?  Three weeks ago I arrived to CM from Bkk on the morning train, and was told at the CM train terminal to self-quarantine and use the app.  Next week, I will be coming to CM, arriving on the morning train again.  I'm just wondering what is practically happening each day to travelers who are arriving, other than "quarantine" and use app.  Information is so scattered here in Bkk, on the one hand I understood I needed a covid test taken in Bkk to enter CM, but the train station here yesterday stated the test was not required to board the train to CM, leading me to believe it must not be required.  Thanks in advance all.