Please Help Create Trigger Condition On Update

please help create trigger condition on update

IF EXISTS
(
SELECT *
FROM empList
WHERE (unit = 9)

)
begin

update [dbo].[empList]
set unit = CASE WHEN SELECT na,empID, unit
FROM empList
WHERE (empID IN (111, 222, 333, 555)) AND (unit = 9))
then '4' else t.fld1 end

i have an emmployee table



empid unit

------------------------------------------------------

1111 3

2222 9

3333 9

4444 2

5555 2

6666 1

7777 9

8888 2

9999 9

-----------------------------

i need help create trigger condition on update like this

ONLY ON

EMPID=2222,3333,7777,9999

WHAN ON UPDATE they have unit =9 THAN

I NEED THE trigger DO THIS



empid unit

------------------------------------------------------

1111 3

2222 4

3333 4

4444 2

5555 2

6666 1

7777 4

8888 2

9999 4



ONLY IF someone update EMPID=2222 OR 3333 OR 7777 OR 9999 and UNIT=9

THAN automatic change 9 TO 4



TNX for the help