I just use the odometer/trip meter in my car to keep track. The hardest part is remembering to reset it when I’m done tracking mileage, not sure how an app would be any easier or more efficient
When I was a rideshare driver, I used QuickBook which was pretty good. The same company that owns QuickBook also owns Turbotax. So, it makes filing tax pretty easier. Anyway, here is a website that might help: