This choke is demonstrated here when your opponent attempts to pass your guard.
Your opponent attempts to pass your guard by coming up on their left foot to create space in front of their stomach. Note that they haven't secured your left bicep, this will help you when applying the choke.
As your opponent slides their arm between your legs, grab it with your right hand.
Now uncross your feet and twist anti-clockwise on your back, pulling on your opponents left wrist will help in this movement. You are aiming to lay your right leg flat on the back of your opponents neck. Also take their right arm across your body as shown, you want their arm in front of their neck.
Place your right foot under your left knee to secure the hold.
To apply the choke keep your left knee bent and place both hands on the back of your opponents head. Now pull down on your opponents head whilst pushing your hips up.