Clean your scalp and keep it moisturized. You can wash your hair in the shower or use a foaming shampoo. If your scalp isn't dry, and you typically collect build-ups, you can also use apple cider vinegar mixed with water to deep clean your scalp. If your cornrows are made together with synthetic hair added, which is treated with highly alkaline chemicals, ACV would also neutralize that. Tea tree oil can also help with itchy scalp problems.