Hi mutsuyuki,
Are you using the devkit or custom board?
Please just follow the steps from official documentation first.
<env-var> is the parameter for different models and is not necessary in this case.
If you don’t assign these parameters, it would just extract them from EEPROM.
There’s also the example command in the link you just refer to.
If you want to know more about the usage of l4t_initrd_flash.sh, you could also refer to the Linux_for_Tegra/tools/kernel_flash/README_initrd_flash.txt.
If you are using the devkit, you could use SDKM to flash into NVMe SSD.