Spool files are unfortunately NOT included in an i5 full-system save, so there is no way to restore them. i5/OS commands are available to copy the spool files to physical files that are then picked up by the system save, but this of course needs to be done before the save is run. Various third-party packages are available that facilitate the process of copying spool files to physical files and then restoring them if necessary. We use Save Output Queue (SOQ) to back up our spool files, and it works pretty well.
Hope this helps.
If you are using BRMS and have saved the spooled files as part of the entire system save then folow the recovery instructions printed with the full system save or consult the BRMS manual. Otherwise Steve is correct that an option 21 ful systems save does not save spooled files.