On mobile: You can find past trips by going to Trips on the sidebar. Here you’ll be able to see Active, Past and Following trips. If you would like to delete past trips select Manage Trips. Select the trips that you would like to delete and choose Delete (to see more info on how to delete trips click here)
On web: Scroll all the way down until you find the Past Trips option.
There is also a See all remaining trips option which loads any active trips not being listed in the main page.