Boot devicej preferences

I have Nvidia Jetson Xavier NX how to chage preferences for boot device?

For example if I have eMMC and SSD can i choose the order from witch the load the Operating System?
and I have another question,
How to clone eMMC Operating System and flash this image on other identical machine ?

Thanks

please refer to

https://elinux.org/Jetson/L4T/Boot_From_External_Device