I am not with Laminar Research; just a flight simmer.
Provided you are not looking for the 3rd party hybrid called steam and previously downloaded X-Plane from Laminar Research then you are in luck.
You need to download the demo version of x-plane from the Laminar Research site at X-Plane.com. The demo version is exactly the same as the full version and will become the full version when you apply the "password key numbers"
Once downloaded you need to collect all you receipt number(s),date of purchase details, acknowledgement details, method payment details etc. When done contact Laminar Research at firstname.lastname@example.org and supply the gathered information including the email address you used at the time of purchase. It may take a few days to get a response as others are doing the same.
When the password is supplied, start X-Plane and apply the password when asked to do so. All should then work.