The event calendar page is unique in that it is not listed in the “Pages” like the rest of your web pages. So to edit it you need to:
Click on “Events”
then on “Settings”
Then click on the “Display” tab
Scroll down until you see “Advanced Template Settings”- Right below that you will see two boxes “Add HTML before event content” and “Add HTML after event content”
The first box
is for everything above
the event calendar / listing
The second box (empty here)
Would add things down below the calendar here