select2

SELECT
  t.orderid,
  RTRIM(
    XMLAGG(
      XMLELEMENT(e,
        blob_to_text_range(
          t.UNDINSTRMTGRP,
          c.start_byte,
          c.end_byte
        )
      ).EXTRACT('//text()')
      ORDER BY c.chunk_num
    ).getclobval()
  ) AS full_text
FROM ZEXECUTION t
CROSS APPLY (
  SELECT
    LEVEL AS chunk_num,
    (LEVEL * 4000 - 3999) AS start_byte,
    (LEVEL * 4000) AS end_byte
  FROM dual
  CONNECT BY LEVEL <= CEIL(
    blob_length(t.UNDINSTRMTGRP) / 4000
  )
) c
WHERE t.orderid = '2524650mm1x'
GROUP BY t.orderid;