The utility first backs up the existing SPL* files (to a separate directory), and then attempts to rebuild them.
SPLREPAIR.bat backup-directory
Run SPLREPAIR from the location that contains your spool control files (that is, the same location as catalog.dat, or the directory indicated by the MVSSPOOLDIR environment variable if the spool control files are stored elsewhere).
SPLREPAIR C:\SpoolCTRL\bkup