I had a similar issue with an event I deleted and created another one that I wanted to point to the same url of the old deleted one. My work-around solution was to redirect the old event url that was deleted to the new event I wanted.
Here is the guide to redirect in SquareSpace: https://squarespace1619507180.zendesk.com/hc/en-us/articles/5863208486541-URL-redirects