To create a template for electronic payments in JPM format, you would need to modify the payment templates in NetSuite. This is possible with the advanced version of Electronic Bank Payments.
You can find the templates in your account if you have the paid version of Electronic Bank Payments. If you need to add specific details or modify the template for your particular bank, you can do so by editing the Freemarker file for the native payment file template.
However, please note that creating a custom format with the same setup as the native EFT one and using it on company bank details may cause an EP0003 error.