I am the scholar of the counter master who is before me and I complete his play. When the player is turned I quickly wound him behind his right arm. And under the coif in the back of the head, or in the cheeks of the arse (with reverence), or the back of the knee, or in any other place that I find uncovered.
The scholar to the counter is not a technically complex play. It shares a lot with the 15th scholar of the 2nd master of sword in two hands, in that it simply demonstrates one of a number of possible ways to follow up on an elbow push.
As the counter to the master of sword in armour, you pushed on your opponents elbow to shove them offline to the right. You have also circled around to your left, leaving you somewhere behind your opponent. You are not striking at a predetermined place necessarily, but just taking advantage of a golden opportunity while it exists.
Make a small step with your left foot. This will in part make any fine corrections to your distance and angle of attack. More than that, as you push off from your right foot, your weight will drop down onto your left. This adds a lot of momentum and power to your attack as you make your thrust into any available target.
Exactly where you attack will vary depending on your opponents armour and the angle you find yourself on. The picture shows an attack to the right armpit, but also suggests sliding the point under the coif and base of the helmet, or driving into the less protected backs of the legs at either arse or knee height.
You have a free strike. Take a look at what is in front of you and make the most of it. Be sure to finish with the remainder of the five things you must do to complete an attack sequence. A good place to start would be to grab their shoulders, pull them directly backwards, and then hammer into their face when they hit the ground.