Hello,
In order to use the RappID Bootloader you need to perform 2 steps:
#1: Flash with S32 Design Studion the Flash Algorithm (the RBF file) into the S32K144 Flash Memory over JTAG interface. The RBF file can be found in the src\tools\BootLoader\RBF_Files folder
For more information please check this: https://community.nxp.com/thread/455356#comment-925112
#2: The application that is supposed to be loaded via RappID bootloader application must be compiled with Bootloaded support from Simulink (select UART as download interface). There are Simulink Examples for this topics.
Best regards,
Daniel