my DB2 is v11.5.7 assume UNIQUEID is the PK of target table
Convert
DELETE FROM targetTable tt
INNER JOIN referenceTable rt ON rt.fk = tt.fk
AND ...
AND tt.UNIQUEID = rt.UNIQUEID
Into
DELETE FROM targetTable x
WHERE EXISTS (SELECT * FROM targetTable
INNER JOIN referenceTable rt ON ON rt.fk = tt.fk
AND ...
AND tt.UNIQUEID = rt.UNIQUEID);
P.S refer to https://www.ibm.com/docs/en/i/7.4?topic=subqueries-example-correlated-subquery-in-delete-statement