You can certainly target sides of your abs. Christ almighty.

The answer is the same as when someone has one bicep larger than the other: the only real way is to stop working out your left side and to work out your right side until it catches up. But this is dumb to do unless if the asymmetry really stands out... you aren't competing or anything, nothing requires you to be symmetric, no one but yourself.

My left side is dominant too, sometimes our muscles are just weird, sometimes our mind/muscle connection works in different places better. I figure if I stick with working out long enough I will just max out the growth on one side and the other will catch up eventually.