You can erase many things related to items you have looked at by going to your Recently Viewed page and using the "Clear all" link there:
https://www.ebay.com/mye/myebay/rvi
That will not affect everything, however.
Your four most recently viewed items also appear on your Summary page. You may also see suggestions on the main eBay page based on recent past searches.
Those can be displaced by performing new searches and viewing new items.
You may also see suggestions based on saved searches or saved sellers. You can control whether those contribute to your feed by going to your Feed page, clicking on the number of saved searches and sellers at the top, then using the sunglasses icon to reveal toggles that control whether the search is used for the feed or not.
You may also want to clear your browser history to erase the record of pages you have visited.
