Google services. Gmail and email calendar integration. How?

Question

gmail

Hello.
The question is this: we have a letter from public services. At the beginning of the letter, a custom calendar is integrated for the date of the event, and shows timestamps about events. Screenshot here

Question: How to integrate the calendar into your letter?
The letter comes with an ics file - when you click the button * add to calendar * of course, responsible for the body of the event. But how to create data output from the calendar in the header? thank!