Need help in UPDATE data in SQL Query

CREATE TABLE test (id int identity(1,1), weeknum INT,ord int,dt1 datetime, wd int)
 
INSERT INTO test VALUES (101,'1','2011-12-20','484') 
INSERT INTO test VALUES (null,'2','2011-02-12','444') 
INSERT INTO test VALUES (null,'3','2011-02-12','444') 
INSERT INTO test VALUES (null,'4','2011-02-14',NULL)  
INSERT INTO test VALUES (102,'1','2013-05-27','544') 
INSERT INTO test VALUES (null,'2','2013-06-02','544') 
INSERT INTO test VALUES (null,'3','2013-06-03',NULL) 
INSERT INTO test VALUES (null,'4','2013-06-10',NULL) 
INSERT INTO test VALUES (103,'5','2013-07-08',NULL) 
INSERT INTO test VALUES (null,'6','2013-07-08','690') 
INSERT INTO test VALUES (null,'7','2013-07-10','690')
 
;with mycte as
(
SELECT id,weeknum,dt1, row_number()over(order by id DESC) rn
  
FROM test A)
 
SELECT m.id,d.weeknum , m.dt1  FROM mycte m
OUTER APPLY (SELECT TOP 1 weeknum  FROM mycte
WHERE  rn>= m.rn AND weeknum IS NOT NULL
ORDER BY rn ) d (weeknum )
  
Order by id

drop table test