How to add/append carousel selection to order preview on actions on google?

I'm trying to make an actions on google app that will be able to order something I want to be able to add anything I select from the carousel to the order preview. I followed the tutorial provided by actions on google for the "book store" (I'll post the link below) but I can't seem to find any tutorial or documentation on how to add carousel selection to your order preview.

Edit To be more specific, this is what I am trying to do:

Users asks:

"talk to my app"
>> "Welcome to the app!"
"I would like to order a coffee"
>> Okay, what would you like to order?
   * Carousel appears with different options
*User selects an option and that option gets added to the bill*
 >> Okay, are you ready to check out?
"Yes"

and from there, the user can see what he or she just selected from the carosuel onto the order preview/ bill.

How would I go about doing this?

Thanks for the help!

link here

from How to add/append carousel selection to order preview on actions on google?