for volumes of type DBBACKUP..try using the DELETE VOLHIST commands to return
them to scratch. It has TYPE=DBBACKUP parameter along with a  TODATE and TODAY
parameters.

These type of volumes are not defined with a DEFINE VOLUME command, so a DELETE
VOL will not help.

I backup my database in full each day to a labeled tape but it is not  a
DEFINED volume but is a recorded one Volume History as a database backup type.
I run a scheduled DELETE VOLHIST command to remove old backups and I can reuse
the tapes. If you issue Q VOL TYPE=DBBACKUP, you should see a list of your
database backup volumes.
Hope I helped.