You can only grow muscles and an entire muscle will grow at once. If you get some growth in that area the whole forearm will be bigger. It's also really hard to make any long term gains via isolation training so I'd venture the best way to make that area bigger is to deadlift, squat, row, and press. The biggest thing I would suggest you tacking is the overriding human desire to find fault with themselves. You have a body, it works, enjoy it, make it better. Trust me when I say that if it wasn't the wrists it would be something else. The best thing you can do is detach yourself from garbage like that. Self obsession and the overwhelming need for acceptance are two major hurdles. They cloud the mind and weaken you. You won't ever completely eradicate them but try to keep perspective and hammer away. Gradually their pull will be lessened to a mere annoyance.