The right bike pedal is screwed on with a standard right-hand thread. The left pedal is on a counter-thread, a left-hand thread. To loosen the left pedal you need to turn the axle clockwise.
Wheels On The Ground
Put the bike on the ground. Put a foot on the pedal to stop it coming up as you pull up on the key. If the pedals have flats and sockets it’s quicker to unscrew them via the sockets once you’ve used the power of the pedal key to unlock them.