You can clear your "Recently viewed" items by going to the "Recently viewed" page and using the "Clear all" link.
https://www.ebay.com/mye/myebay/rvi
If you want to clear selectively, I believe you can do that via the eBay app.
Note that this may not prevent some items from appearing on the main eBay page or on your Summary page. You may see recommendations based on past searches that can be displaced by performing further searches. You may also see recommendations based on your Saved Sellers or Saved Searches.
