If you are going to use an Arduino Mega, you have to edit everything on this sketch that says "Serial" and replace it with "Serial1" (or whatever number you are using ...

1-) Open nextion editor and create two button b0 and b1. 2-) Set b0 touch press event print 1, and touch release event print 0 3-) Set b1 touch press event print 3, and touch release event print 2 4-) ...