Go to the .my Domain Registry Domain modification page:
https://web.domainregistry.my/Mynic-ViewController-context-root/faces/PB/UserLogin.jsp
Enter Domain name, select Domain extention and click modify
Select login as "Administrative Contact", enter administrative user ID, password and click "Login"
After login, click "Option 3" (Appoint A New Administrative Contact)
Go to item 1 (Appoint A New Administrative Contact)
Enter your Administrative Mynic handle or enter new information if you dont have .my Domain Registry handle.
Clicl "Modify" to confirm your change