To fix corrupted Winrar files, first identify which files are corrupted by opening them individually with Winrar until it gives an error message. Next, open the corrupted file, press ALT + R, select "Treat currupt archive as RAR", click OK, and the file should be repaired. Move the corrupted file to a safe location, rename the repaired file, and try extracting again. This method only works on RAR files that contain recovery records.