I have purchased a 20A immersion heater switch with no paperwork included.
Can someone advise me how to wire it?

Looking at the back of the switch there there are three terminals on the
left side:
Earth,
L2
L1.

On thr ight side, there is:

Earth
N2
N1


Which wires from the two 3-core cables (mains feed cable and immersion
heater cable) go where?

Thank you.

Al