I think the original is L4T R23.0.1, but the earliest available is R23.1. I would not recommend this unless you have a good reason for it…probably R28.2 is the best choice if you don’t have some requirement for the earlier releases. R23.x wasn’t even 64-bit user space.
There isn’t a true “factory reset”, but you can flash to any of the available versions.
JetPack is a front end for flashing and for additional packages. Flashing itself uses the driver package plus sample rootfs. You can use the driver package plus sample rootfs on any Linux PC host to flash the Jetson, or you can let JetPack download this and operate the flash for you. Command line flash isn’t actually too difficult, and JetPack will imply you need an Ubuntu 14.04 or 16.04 host. You can use JetPack at any later date and uncheck flash to simply add packages.
A list of older L4T versions is here, but you’ll need to go to that URL, log in again (registering is free and does not produce any spam…you might need to register a second time in addition to forum registration…and after login in click the URL again):
JetPack versions are listed here:
There is official documentation with each release, but here is a digest of command line flashing (adjust file names for release version):
I don’t know which L4T version goes with which JetPack, but if you look into the JetPack documents it should name the L4T version it supports.