This technique is used when your attacker grabs your collar.
Your attacker grabs your collar as shown.
Firstly grab your attackers right hand with your right hand to pin it where it is.
Step forward with your right foot so you turn sideways on to your attacker and strike with your right elbow to their right arm to force it to bend.
Straighten your right arm and step forward with your left foot so you are now no longer sideways on to them.
Bring your right hand under your attackers arm and place it high up on their chest. To apply the lock simply raise your right elbow and straighten your arm slightly.