You’ll need Barkeeper’s Friend fine pumice, heavy-duty scrub pad and water.
Sprinkle the pumice on your rusty disc, add a little water and work it into the disc with the scrub pad (circular motion works best).
After about a minute or two, your disc will be free of the topical rust.
Wipe down with a clean paper towel, then again with a damp paper towel.
You’re now ready to season again and get back to cooking.