tx2 could not be started

I changed the tx2 system configuration file, but tx2 could not be started. Can I access the hard disk and change the file back?

I’m not sure what system configuration file you mean, but you have a couple of options. The brute force method, which always works, is to clone the rootfs, loopback mount it on the host, edit the loopback file system, and then re-flash telling it to use the edited rootfs instead of the sample rootfs. This is very useful since you have an off-system backup to reference later (and this loopback mounted file can even act as an rsync destination), but is quite time consuming.

You could also create a rescue SD card, boot to that, mount “/dev/mmcblk0p1” on some temp mount point (SD card rootfs is mmcblk1p1, eMMC rootfs becomes an unused partition), edit, shutdown, remove the rescue SD, and then boot back up fixed. This is fairly simple if the config did not alter the boot environment.

In all cases you would be advised to have a serial console cable handy for options (e.g., picking from multiple boot configurations). See:
http://www.jetsonhacks.com/2017/03/24/serial-console-nvidia-jetson-tx2/

Here are some related posts…just ask if you want more information, some of it may be out of date:
https://devtalk.nvidia.com/default/topic/1018963/jetson-tx2/jetson-tx2-doesn-t-startup-after-installing-tensor-flow/post/5188175/#5188175
https://devtalk.nvidia.com/default/topic/1019599/jetson-tx2/jetson-tx2-rebooting-due-to-corrupted-rootfs-any-pointers-to-recover-it-/post/5204740/#5204740
https://devtalk.nvidia.com/default/topic/1019599/jetson-tx2/jetson-tx2-rebooting-due-to-corrupted-rootfs-any-pointers-to-recover-it-/post/5190948/#5190948