Do you mean you deleted all the items on your Watch List?
If so, I do not think there is a way to undo that other than finding those items again and adding them back individually.
You may want to check your Recently Viewed page:
https://www.ebay.com/mye/myebay/rvi
You may also want to recreate some of your recent searches to see if you can find the same items once more by performing the same search.
