Using a desktop browser, go to your Saved Searches page:
https://www.ebay.com/mye/myebay/savedsearches
Use the "More actions" menu on the right side of an entry to Unsave the search.
If you are using the eBay app, use the three dot menu on the right side of each search entry. You may have to scroll the menu up to see the Unsave option at the bottom.
