From this link....
https://coronavirus.health.ny.gov/covid-19-travel-advisory#overview
“To file a report of an individual failing to adhere to the quarantine pursuant to the travel advisory click here or call 1-***-***-****.
Individuals may also contact their local department of health.”
Asterisks are mine.
Web address and phone number need to get out there for some heavy duty DOS flooding courtesy of 4Chan and others.