Yes, of course I read. Nothing has said how to actually do it, though.
It depends on what client you're using to download the torrent. Most have an option somewhere to tell it to re-check what data is already present. In my own client of choice, uTorrent, you right-click on a stopped torrent and select "Force Re-Check" from the context menu. The location of the option to force a rehash of data differs with each client, although I imagine most would be in a similar part of the program as uTorrent.