If the shoes you are wearing have some sort of heel (like work boots), you can probably use regular bike shoe covers.

If they don't, shoe covers don't work because they have to wrap across the bottom of the shoe somewhere, and on a shoe with a flat bottom that means stepping on the strap constantly - which will quickly wear through it.

It's usually easiest just to buy warmer shoes. Wool socks and thicker wool socks help as well.