It should have been sent to you around the end of January if you had a claim already. If you haven't received anything, you can have a look at the website and call the phone number which is displayed on the page. They will be able to tell you how to proceed.
You should have received this already. If you didn't , you can go to this website and read the information there - follow the link in blue to find out how to claim your form or use the Contact section to speak to someone directly.