Another method that is applicable to all kinds of platform.
1.Mount the APP partition
mount /dev/mmcblk0p1 /mnt
2. Add the boot args
For T210 (Jetson Nano/ TX1)
sed -i "s|^\([ \t]*APPEND \${cbootargs}\) .*|\1 root=/dev/mmcblk0p1 rw rootwait rootfstype=ext4 console=ttyS0,115200n8 console=tty0 fbcon=map:0 net.ifnames=0 sdhci_tegra.en_boot_part_access=1|" /mnt/boot/extlinux/extlinux.conf
For T186 serise (TX2/TX2i/TX2-4GB)
sed -i "s|^\([ \t]*APPEND \${cbootargs}\) .*|\1 root=/dev/mmcblk0p1 rw rootwait rootfstype=ext4 console=ttyS0,115200n8 console=tty0 fbcon=map:0 net.ifnames=0 isolcpus=1-2|" /mnt/boot/extlinux/extlinux.conf
For T194 series (NX/AGX Xavier)
sed -i "s|^\([ \t]*APPEND \${cbootargs}\) .*|\1 root=/dev/mmcblk0p1 rw rootwait rootfstype=ext4 console=ttyTCU0,115200n8 console=tty0 fbcon=map:0 net.ifnames=0|" /mnt/boot/extlinux/extlinux.conf
3. Unmount APP partition and reboot
umount /mnt
reboot