With the crank in the position closest to the front tyre (horizontal and forward), put your allen key in the socket while aimed at 12 o'clock (ie, upward) and r

With the crank in the position closest to the front tyre (horizontal and forward), put your allen key in the socket while aimed at 12 o'clock (ie, upward) and rotate toward the rear of the bike. The rule is basically: rotate against the direction of the crank's rotation to undo.