How do you fill this part of your arms with muscle?

I'm doing the following once or twice a week, but still this part of my arms (see attached) gets very little progress: 1. Chin ups 2. Push ups 3. Tall kneeling pallof press 4. Seated external rotation 5. Lateral raise 6. 1-arm dumbbell bench press 7. EZ-bar curls 8. Close grip push ups

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