How should i wire this correctly? Double Switch?

Hi, I have a double switch by my front door. Currently the switch on the right is working the main light in the lounge (this is also on a 2 way with a switch ont he other side of the room) the other switch is not wired up at all (i think originally it was connect to an outside light but all wires ahve been removed). I want to use this switch to run an ourside porch light independently - how should i wire this up? The switch has 'com' L1 & L2 in a triangle shape behind both individual siwtches.

Thanks all,
Rob