By stopping mail-in ballots.
I doubt that genie can be put back in the bottle. At least Illinois has voters request a ballot by mail or via a web page. You identify yourself by signature, DL #, or last 4 digits of SS #. You sign the ballot envelope and then mail it in or place it a drop box. It is slight better than just sending out ballots to people on the voter rolls. If one believes Chicago vigorously checks signatures, I'll have a bridge to sell them.