Hi Bahia,
If you already gave the special offer, price breakdown should be available on the left side of the page specifically on your message thread with the guest. This is using a browser.
As for the guest interface, they will see a button for special offer on their browser or app in the center of message thread as well as there will be email notification for them that you (as a Host) offered them a special offer. They just have to click the "Special offer" button and "accept" to book the property.
I hope this helps.
All the best,
Upfish Management