Two-pin plug in three pin socket

Use a sharp object (e.g. screwdriver) and insert it into the neutral port (bottom-left). Simultaneously, insert the right pin of your two-pin plug into the live port (bottom-right). Then, remove the sharp object while inserting the left pin of the plug into neutral port as usual.

CAUTION: Do not insert any sharp object into the live port (bottom-right) as you may be electrocuted. Turn off the switch before attempting any of this.