downloading ce flight

I am currently opted in for Halo Insider program and I haven’t gotten any email about Halo:CEA flight how do I download Halo:CEA flighting

You can only play the flight if you’ve been invited to it, which being enrolled in the program does not guarantee.
Check your email (the one you verified while signing up), if you don’t have anything from inviting you to the flight then I’m afraid you weren’t picked this time around.