Have I forgot which way round already ffs?
To undo:
Crank horizontal, pedal towards the front of the bike, spanner horizontal, towards the back of the bike, and press down (taking care to keep the knuckles off the chainring).
Whilst I'm sure
@steveindenmark know what he means, this is the same direction that the pedal axle would turn if the pedal bearings suddenly seized when riding.
The loosening mechanism (precession) works in the opposite direction, so you need threads that unscrew when turned in the pedalling direction.
Loosening probably mostly happens when someone installs normal cranks on a crossover drive tandem, rather than paying out for a specific tandem crankset.