Convert RAK4631 to Zephyr bootloader

I am working with Zephyr RTOS and I would to prepare one of my RAK4631 with a Zephyr bootloader.

In the RAK4631Sidewalk version , we have a Zephyr bootloader.

I know that in the RAK4631 documentation we have instructions how to flash a new bootloader using Nordic nrfutil: Converting RAK4631-R to RAK4631. I would like to do a similar task but instead of Arduino bootloader, a Zephyr bootloader, like RAK4631 for Amazon SideWalk.

Could you help me?

Regards,

Claudio Rosa