There may be apps out there that will help, like Fooducate, but working directly with a renal dietitian may be a better choice. My Mayo dietitian meets with me every 3 months and has laid out a plan to follow so that my eGFR trend remains stable. Nephrologists unfortunately hardly ever talk about eating the correct foods
and exercise. There are plenty of great books as well from non profit kidney organizations or other best sellers. By using an app, you will find that there will be more questions, which can be solved best by a renal dietitian.