Not sure what you mean with the "startm7 command" (but mayber that is because you did not explain the context...)
Anyway: when you use the bootloader, you configure which image to be started on which core in the EB Tresos tool. It is described in AN13750.

What the generated bootloader source code internally does is to use the MC_ME engine of the S32G2 to prepare start addresses for the respective image fragments and then release the cores from reset. you don' t need to do this yourself if you use the bootloader.If you donÄt want to use a bootloader like this, you have to implement the logic yourself.