Modifying SQL 2008/2012 PARTITIONS

Dear Experts;

My client has asked me to extend a project past it's expected end date of 2016.  The database has PARTITIONS through 2017 and I need to extend or create new PARTITIONS through 2020.  The problem I'm having is with the ALTER SCHEMA and FUNCTION - I just don't know what to do.  I have the ALTER DATABASE to create the FILEGROUPs example below, but cannot figure out the syntax for the SCHEMA and FUNCTION.

Experts, I need your help.  The original script that created the PARTITIONS AND SCHEMA is attached.

Thank you!

IF NOT EXISTS(SELECT * FROM HARBOR.sys.filegroups WHERE name = 'HARBOR20181001')
BEGIN
  ALTER DATABASE HARBOR
    ADD FILEGROUP HARBOR20181001

  ALTER DATABASE HARBOR
    ADD FILE ( NAME       = N'HARBOR20181001',
               FILENAME   = N'C:\Data\HARBOR20181001.ndf',
               SIZE       = 2048KB,
               MAXSIZE    = UNLIMITED,
               FILEGROWTH = 1024KB )
     TO FILEGROUP HARBOR20181001
END
Harbor.sql