Q.drainage
I have a grass area approximately 18’X 24′ that is about 4″-5″ lower than the rest of the garden. After heavy rainy days or periods it is flooded. I am looking for advice on how best to remedy the flooding, hoping to find a product(s) to mix with soil to top up the area. It is hoped that there is something that is inexpensive that would reduce if not eliminate flooding.
Thank you.

This article may help you.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/yard-drainage-problems.htm