You want to purge and recover space from the data files that are already full.

Relevant versions:  ALL

When you delete an incident, DLP will mark it for deletion within the DB and DLP will purge it during the scheduled purge (usually midnight). After the data is purged, Oracle will reuse the space for new incidents. 

To clarify, Oracle will not surrender space that has been explicitly allocated to it.  With the deletion and subsequent purge of incidents through Vontu, individual records are deleted from the database, but the database size will not shrink.  The space released through deletion is re-used by new records and database growth is non-apparent until all useable "freed-blocks" are consumed.

For more information about incident deletion, see this article: Why doesn't the database shrink after incidents are deleted? (broadcom.com)