How to get your lower bicep bigger?

Honestly Genetics has a big role in how your muscles look. For example, my bicep doesn't have a peak, instead its just big but straight across and only slightly curved. But try alternating curls, instead of doing dumbell curls and barbell curls do hammer curls and preacher curls, or even drag curls. Make sure your biceps are doing all the work, only move your forearm, your elbow(s), back and shoulders should not move. Contract and squeeze the muscle as hard as you can for 1 second, at the top of the movement, and lower the bar/ dumbells SLOWLY, about double the time it took you to lift the weight