The dataentry of the 16M version shows U-Boot web recovery as a recovery method, and gives the following comment:
Unplug power, press reset and plug power, then go to
http://192.168.1.1and press center button
Please try this and report back.
Edit: This topic might also be of interest to you: Need assistance with recovering a ZBT-WG3526
Edit #2: And you should really find out if you have a 16M or 32M device (see topic linked above)