Next, go to New -> S32DS Project from Example. Enter s321R274 in the search field. You should see example projects 'flash_program_erase_s32r274' and 'eeprom_emulation_s32r274'.
Then, if you clear the search field and scroll to the bottom of the list, you can see the example project 'BootLoader_MPC5748G'. Though it is for the MPC5748G and not S32R274, it should provide some reference to you on creating a bootloader project.