The application is on the district's website along with these instructions:
If Ballot is to be Mailed: Must be RECEIVED NO LATER THAN SEVEN DAYS BEFORE ELECTION OR May be filed IN PERSON through the day before the election (December 9, 2019) to The District Clerk, North Shore Central School District 112 Franklin Avenue, Sea Cliff, New York 11579
The application can be downloaded here, picked up from the district office or mailed to you by calling the district clerk.
The district's bond information flyer posted here indicates that once you have the ballot, "The deadline for receipt of absentee ballots by mail or personal delivery is December 10, 2019 at 5 PM."