Adjust ONLY right or left margin

Hi,

I'm new to the forum. Recently my Kindle 4th gen developed a crack in the screen in the bottom right hand corner, making it impossible to read. What I'd like to do is increase the right margin, while decreasing the left margin - in essence shift the entirety of the test to the left.

Is this possible? I know I can change the horizontal margin for both sides, but that only allows me to make them the same size.

Thanks,
A