Update avg value in table - sql

Question

I'm tring to update my mark average by adding to it some value.
My table of admited student contains (NOSTUDENT, COURSECODE, SEMESTER, NOGROUPE,MARK) Columns.
My View : AverageByGroupe contains the average of mark of students following that course in corresponding semester.
CREATE OR REPLACE VIEW AverageByGroup AS
SELECT COURSCODE, NOGROUPE, SEMESTER, AVG(MARK) AS AVGMARK
FROM ADMITED_TABLE GROUP BY COURSECODE,NOGROUPE,SEMESTER;
Question: I want to update the average mark for a given course, group, semester by 10, but AVGMARK is note a column, What it the correct UPDATE syntax.
What I have tried:
UPDATE ADMITED_TABLE
SET AVG(MARK) = SELECT( (AVG(MARK) + 10)
FROM ADMITED_TABLE WHERE COURSCODE = 'AAAA'
AND NOGROUP = 2
AND SEMESTER = 'AUTMN');
Error:
Error de command ligne: 2 Column: 8
Rapport of error -
Erreur SQL : ORA-00927: missing equal sign
00927. 00000 - "missing equal sign"
*Cause:
*Action:
Edit:
To be more clear, this is a mutate table so what I want to use is a INSTEAD OF INSERT TRIGGER wich fire every time the mark average is chaged by adjusting that cours student mark.
For the select syntax error, I included select in (
UPDATE ADMITED_TABLE
SET AVG(MARK) = (SELECT (AVG(MARK) + 10)
FROM ADMITED_TABLE WHERE COURSCODE = 'AAAA'
AND NOGROUP = 2
AND SEMESTER = 'AUTMN');
Error:
ORA-00927: missing equal sign
00927. 00000 - "missing equal sign"
*Cause:
*Action:

Answer 1

UPDATE NewADMITED_TABLE
SET AVGMARK = (AVGMARK + 10) -- this is not a DERIVED column anymore
WHERE COURSCODE = 'AAAA'
AND NOGROUP = 2
AND SEMESTER = 'AUTMN