What is the right way to run fw_setenv for selecting different ECC or dtb files?

[Jupiter]

Hi,

To flash u-boot to iMX6ULL NAND, it requires using higher bits ECC (my
imx6ulz_kobs.dtb) to run kobs-ng in ramdisk, but to flash rootfs image
to NAND in ramdisk, I have to change to use lower ECC (my
imx6ulz.dtb).

I followed the advice at link
https://developer.toradex.com/knowledge-base/u-boot-fw-utils to run
"fw_setenv fdt_file imx6ulz_kobs.dtb" before flashing u-boot to NAND,
although the fw_setenv command worked, the u-boot wasn't installed
properly in NAND, I could not boot from NAND.

What is the right way to run fw_setenv for changing different ECC or
different dtb files?

Thank you.

Kind regards,

- jh

-- 
"A man can fail many times, but he isn't a failure until he begins to
blame somebody else."
-- John Burroughs