You have your opponent in your guard and are holding the left side of their collar with your left hand (fingers inside, thumb outside).
Grab their collar with your right hand (thumb inside, fingers outside) just to the left of your left hand.
Pull your opponent down to your chest with both hands. Uncross your feet (if using the closed guard) and put your right foot on the ground.
Put your weight on your right foot and left shoulder, lift your hips off the ground and take them to the right. Keeping your left elbow down, take your right arm over the top of your opponents head.
Twist your right wrist clockwise and push your elbow down to the side of your opponents neck.
Cross your feet again to put your opponent back in your closed guard. To apply the choke push your right elbow away from you.