OK, I moddified the SQL a little am an getting closer. this is what I am using

UPDATE TRX
SET "Discipline"='SBP'
WHERE "Id" IN
(SELECT "Id"
FROM APPOINT, TRX
WHERE APPOINT."Date"=TRX."TreatmentDate"
AND APPOINT."Patient"=TRX."Patient"
AND APPOINT."Clinic" =1320
AND APPOINT."Type" IN (0,1,2)
);

this update 378 rows. However the select by itself anly grabs 377 rows. I am not sure why it is updating one extra row. Any advice on that?