Try these:
https://www.youtube.com/watch?v=REzz-My2PoI#t=100
https://www.youtube.com/watch?v=Joo90ZWrUkU#t=20
https://www.youtube.com/watch?v=Q8Tiz6INF7I
It takes practice. Newer dancers clap on 1 & 3 until they learn. Sometimes all it takes is for someone to clap quite loudly (almost passively-aggressively so) on the 2 & 4 for the rest of the people to shift over.