Is there a cure for sickle cell trait?

No. And no cure is needed. With rare exceptions sickle trait has no impact on health and longevity.
There is no cure. Those with sickle cell trait have both normal hemoglobin (hemoglobin A) and hemoglobin S. This means the person inherited a "defective" gene from one parent and a normal gene from another parent.The defective Hemoglobin S gene creates abnormal hemoglobin and sickle shaped red cells. Unfortunately, there is currently no cure for sickle cell disease or trait (As is the case for most genetic disease)
Not needed. Sickle cell trait almost never is is associated with any clinical problems more severe than enuresis (bed wetting), so there is no need for a cure. If your question is whether the gene mutation can be reversed so you cannot transmit the condition to your children, the answer is no.