I have created a trigger like below.
But it shows me a error. 

```
 2/30    PLS-00103: Encountered the symbol "=" when expecting one of the following:
          := ; not null default character

```

Can anyone help me solving this?
Thanks in advance

```
CREATE OR REPLACE TRIGGER ADRAKLIVE.TRG_HELPDESK
AFTER UPDATE
OF STATUS
ON ADRAKLIVE.TBL_SERVICEREPORT 
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
     declare ts varchar2(10) = :'YES';
 UPDATE tbl_ithelpdesk
       SET it_closed  =: ts
     WHERE call_no = :NEW.call_no;
END;

```