There are no diets that lower the serum creatinine and improve kidney function. There are diets that can slow the deterioration in kidney function. I am a strong advocate for the DASH diet. You can review the DASH diet at: https://www.nhlbi.nih.gov/health/health-topics/topics/dash
It is most important that your husband continue to consult with the physicians who are caring for him. He will be at significant risk for acute kidney injury if there is a major operation to repair his aorta.