Take it off, brush off the rust on the surface with a wire brush, then coat it with antirust paint, and then coat it with a topcoat close to its true color. Because at the bottom, you can't see it, and it doesn't matter if there is color difference.
Just buy a substitute. This is relatively simple. You can call after-sales, or you can contact after-sales and go directly to the business hall to buy it. It is not difficult to replace it. It's just a matter of a few screws.
Make a board out of plastic board, etc. And glue a piece of flannel on the inner surface to absorb sound. The function of this board is to absorb sound and prevent rats, but the material is not a problem.