SQL Attachment For Media Object

Hello - I am able to SQL query for media object attachment using the below query.

SELECT UTL_RAW.CAST_TO_VARCHAR2(DBMS_LOB.SUBSTR(GDTXFT,2094)) AS READBLOB

FROM TESTDTA.F00165 WHERE GDTXKY='200026'

Now, I would like to update the same media object to a constant value say "ABC" using SQL .

I tried using the update statement but it is throwing errors.

Any help to have the right SQL statement.

Best Regards, Harish