Regain access after loss of IP connectivity (ZT instance still connects to Central)

Hello everyone.

A colleage has a Teltonika RUT955 (OpenWRT-derived firmware) with ZeroTier on a remote location, connected with DHCP via its WAN port to another 4G/LTE router, which gives access to the 'net. The chosen IP for the RUT955 was 192.168.30.1, a route was added to access local network 192.168.8.0/24 through it, and the corresponding rules to bridge networks and no auto-IP assign were enabled in Central. Everything worked perfectly.

Last tuesday we were doing changes on the RUT955 webUI and my colleage did a big blunder: changed the WAN port to act as LAN, and manually bridged the ztxxx network to the local lan. Upon doing that we instantly lost remote access to everything, and no amount of fiddling on Central helps. For all intents and purposes we lost all IPv4 connectivity because of a bad routing setting.

Now the thing is, the ZeroTier instance on the router still connects OK to Central: responds to IP changes, shows last time connected and client version etc. So there is some connectivity from outside, just restricted to the ZT instance it seems.

Assuming said scenario: Is there ANY way of reaching the router to undo the changes? (we had SSH access). It’s over 300km to the site, so any help would be greatly appreciated… Thanks!