The normal reset methods won't work because the ext4 type installations don't have a ROM partition. The ROM partition would contain the stock files and configuration (or in some cases, the scripts that are run on firstboot to generate some of the config files). With no ROM, there's nothing to fall back to.

The only way to truly reset everything is to rewrite the storage with a fresh image.

If you use a squashfs type installation, you can use the typical firstboot -y && reboot method to reset to defaults.