Dimmer/Einbau RSLW2 radio switch connection - two black wires in the box

Hello Gentlemen I have a problem as I am a carpenter by profession I prefer to make sure my question is as follows I want to connect a radio wall switch but I encountered a problem and I do not want to spoil the switch in my flush-mounted box there are only two wires of course I do not know what macher did it but the colour of both is black finding the phase is not a problem but here the question is where to connect these wires to the switch which has as many as 4 available places I attached a scan from the manual and if someone would tell me where to screw the phase and where zero? Please help

If those two wires were connected to the switch, I have to worry you - you don't have two wires there, but one. You have an old-style installation where the neutral wire bypasses the switch box.

You need to look for a wireless dimmer that doesn't need a neutral wire (there are some).