I am not sure this is the solution.
Did you set up a password for access on the Cerbo via LAN. Settings > General > Access & Security > Local network security profile - is this set to secured. You may not get these menu items if you are on old firmware.
If you did and can not recall it then Section 8.4.2 in the manual (linked below) describes how you can reset all wifi / Bluetooth / network to Factory settings using the push button. This may clear.
If all else fails then a factory reset as described in the manual could be used to start again.