How should i even out the size of my right arm so that it is just as thin and tone as my left arm?

I use my left arm more than my right causing it to be much more toned and thinner then my right. How can I even out the size of my right arm without neglecting my left arm? What kind of exercises should i do and how do i go about doing it? About how long does that normally take to see results?
Answer:
Switch hand when you master bate

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