Here’s a few quick things you can do when you’re beneath your opponent’s north south position and your arms are trapped between his.
The grappling dummy used in this video is the Submission Master from https://grapplingdummy.net.
A typical thing that could be happening is your opponent going for a kimura shoulder lock from this position.
Often, he’ll go to side control first so he can get a grip on your wrist, then back to north south.
So, if he’s going to side control, you can just pivot with him to prevent that and prevent him from getting a grip on your wrist.
Or, you can bring your leg up and grip it with your arm, which makes it difficult for him to do the kimura lock.
Also, you can use your knee behind his elbow to drive his elbow up as you escape your own arm down to the ground.