Replacing an external sensor with a switch with 3 core plus earth cable

Hi

I am trying to replace an external Greenbrook PEC1000/PECH sensor with an external switch. The cable is a 3 core plus earth and the black was wired up to the "low" connector in the sensor.

Can anyone please advise on how I can wire a switch directly to the 3 core cable? I have tried every combination without success. Can I connect a switch straight to existing cable and lights or do I need to install a PIR and then a switch?

Thanks in advance for your help - I'm new to this!!