Many thanks for the tip.
I tried it, pressed the power button for 10 seconds. Error still as described above.
Then pressed the switch button for 10 seconds, no change here either.
The tutorial from Zeus Mining did not provide any further help either.

Unlike the Nano 3, the new Nano 3S apparently has built-in Bluetooth, but the WLAN transmitter/receiver is no longer in the miner-unit, but is included as a USB-WiFi-module. I tried using a different USB Wifi stick from Fritz.Box, but this also failed to establish a connection.

Unfortunately I get no help at all from Canaan. Two support requests from me have gone unanswered for more than a week now.