I'd start with the physical level before addressing the psychological level, because it's simpler to address, and will likely make the changes you want.
Consider eating high protein, high fat foods. Drink a lot of whole milk. Lift weights daily and exercise. Be efficient with your lifting (focus on deadlift, overhead press, bench press, and squat) Take a break from smoking pot and other drugs.
Yes, this is totally bro science, but I can build up a scientific argument that muscle growth will increase testosterone levels, which in turn will lead to more aggressive behavior.
Or if you want a simpler solution, just get on testosterone replacement therapy. You'd want to consult a medical professional before supplementing testosterone.
I'd suggest focusing on being more confidant and assertive, rather than trying to harbor self-resentment.