Difference in size

My right arm is 1" bigger than my left because I am right-hand dominant. My forearms are a 1 ½" different. What can I do to get my left arm up to par with my right?

Your best bet is to train using unilateral movements. Rather than using a barbell for all your upper body movements, try using dumbbells and also go at it one arm at a time. This is common to have strength imbalances when you place too much emphasis on bi-lateral training. here is a video for some tips.