CalendarView action button forward and backward

I'm working with the Calendarview library

link

And the people there walk around a bit without communication, so I'll ask here.

  

I'd like to take action when switching months, for example   the marked dates of the current month only when you click the   move forward or back.

I would not like to change the original library, so I find it tricky to get the click of the button.

Thank you in advance.