You will need to obtain a Mailer ID from your BMEU (Business Mail Entry Unit), generally the post office where you enter your mailings. The Mailer ID is included in the Intelligent Mail Barcode, along with the same information you have in the PostNet barcode. The Intelligent Mail Barcode also includes a barcode identifier, a service type identifier and a serial number. This information is usually generated and properly encoded and formatted by your mail list management software. If you don't use software, it will be more complicated than printing a PostNet.
The USPS has some good information at https://ribbs.usps.gov/onecodesolution/ that can help you understand what you will need.
