You need to determine which of the Browns is a permanent live.  This is best done with a meter.  Once you know which the permanent live is, you connect this to an
L1, and bridge both L1's together.  The two other Browns then go to the wavy line terminals (one to each).  If the switch works with the left/right in the wrong place, swap the wavy lines around, or turn the whole switch upside down.

Working out which is permanent live is tricky without a meter.

You could connect two Browns together with a terminal block, leaving one live unconnected and isolated from everything (metal back box etc), standing clear, turning power on.  If no lights come on, the UNconnected live is your permanent.  If a light does come on, switch the power off, and choose another two Browns until you find a connected pair that do not cause a light to light.  You then know the UNconnected core is your permanent live.

If you don't feel confident with doing this, dont!  You are essentially turning the power on with live wires exposed, which is not te safest, especially with kids and others running around etc.