You have to be a member of D23 to get the deal. Apparently it is free to join. I'm not joining and not paying Disney for Disney+. I do know that reports are that they have already crashed pretty hard under the load of early subscription attempts.
It looks like you just follow the steps on the big image when you go to that link:
Given it may take 36 hours according to that image for the link to show up, I'd join earlier over later if you want the service.
Louis L'Amour, “To make democracy work, we must be a nation of participants, not simply observers.
One who does not vote has no right to complain.”
Visit our archived Minecraft world! | Maybe someday I'll proof read, until then deal with it.