How can I change the URL of Website submenu pages for Events?

I duplicated an existing event in an effort to reuse some already designed elements. Now my Introduction page for this new duplicated event retains old URL:

event/new-event-title-date/page/introduction-old-event-title-date-copy

I tried to mess with Event's menu but changing URL there only changes redirect action for when menu element is clicked. Not an actual URL of the page so I get 404. I searched for this page under Pages in the Website menu and it is not there.