Korean fans learn the chants before the show

In a Korean concert hall the audience is not there to watch. Every song has its own call-and-response pattern, and it is called the fan chant.
The order the members' names are called in, the lines the crowd answers with, even the parts that stay quiet, are all fixed. None of it is improvised.
One to two weeks before a show, fan accounts post chant guides. Search the group's name with 응원법 on X and you will find videos with the words and the timing on screen.
You do not need all of them. Five to ten of the best-known songs will carry you through most of the night.
The official lightstick connects by Bluetooth to the venue's control system. That is why a whole hall changes colour at once or moves like a wave. Nobody is doing that by hand.
An overseas fan who joins in even partly is noticed immediately by the people beside them. It does not have to be perfect.