To change the ownership of reports in discoverer try the following.
1. Make sure noone is accessing discoverer.
2. Find the internal discoverer user id
3. run the following ...
update eul5_documents
set doc_eul_id = [new disco user id],
doc_created_by = [db user id],
doc_updated_by = [db user id]
where doc_eu_id [old disco user id]
4. verify by logging into discoverer and checking that ownership of reports has changed.