Add event to native calendar crossplatform

Dear readers,
i have a question how do i add a event to the native calendar crossplatform i tried
a github project but its not building in my current project.
https://github.com/rid00z/Xamarin.Forms.Calendar
if i tried it that way i gives me compile errors on NativeRender and CalenderPicker.

Does someone has a clue how to do it ?

Thanks in advance,
Stefan