First, you need Composer.... if you don't have it, you can't build it.
Find a switch or other device in your system that you aren't using or you can trigger inside of Alexa today.
Create a condition that if that device is triggered, or turned on, it will trigger the Card Access devices at the same time. Turn it on, it opens the doors because of the conditions. Turn it off, and it triggers to close the doors. The solution is shockingly simple, but elusive -- and requires Composer.
In the Alexa app, make sure primary device is enabled and can have commands voiced to it. C4 does everything else behind the scenes on the controller.
Hope that helps!