Hello, I can help you get going in the right direction.
Not sure how CF7 works, but you could run a loop to get all the past events and then display the titles in a select box as options.
$pasted_events = tribe_get_events( array(
'eventDisplay'=>'past',
'posts_per_page'=>-1
) );
That will get all the past events and then you could run a foreach loop to create your select box options.
Here is an article on queries that shows the foreach loop and a more complex query:
https://theeventscalendar.com/queries-and-pagination/
To make sure CF7 is the correct tool I would look for a way to use php to fill data into a field first.
Let me know if you get stuck on something or would like some more information.
Thanks