As far as i know, the early release / beta has opened for Chinese and Indian Veriants. The way it worked for me is - under system update settings (the cog at the top right corner) has Trial version settings. Go there. If there is early release for your device, you will be able to see it there. Then you can opt into it by reading their terms and conditions and then providing them with your phone number or email id. That's it. I don't think there is any other process of filling any forms etc.