Hello @Adithya,
Because this app note is a little outdated, I highly recommend check the "MCUXpresso Secure Provisioning Tool User Guide v.8", in order to obtain updated information. Inside this user's guide you can find the chapter 6.2.1.3 called "Image running from external SDRAM", where shows the steps to getting a bootable image from SDRAM using MCUxpresso IDE.
Consequently, in the chapter 6.2.3.1 called "Booting unsigned image" shows the steps to write an image from Secure Provisioning tool V8.
Also, if you experience any issue, do not hesitate to let me know.
BR
Habib