Resetting involves powering it off and on and waiting till the blue light (at the back inside next to the network connector) starts flashing, then pushing in the tiny reset button next to the connector which will make it flash much faster. After that it's ready to connect to at 192.168.1.1. Set your laptop to 192.168.1.2 and plug the ethernet cable into it.

Then do the following:
ssh 192.168.1.1 -l root
mount_root
mtd -r erase rootfs_data

After it reboots it should be back in failsafe settings and you can log in via ethernet again on 192.168.0.100 and flash it with a good firmware.