Let’s assume that you wish to scan the existing Watchlist, or at least part of it. Here is what you need to do.
Open the Watchlist.
Select multiple symbols and choose the Flag All Selected option from the menu.
Go to the Screener and enable filtering by flagged symbols (please note that only the symbols that are traded on the market you selected in the Screener's filters will show up).
Customize the columns by removing undesirable ones and adding the ones you need.
Filter and/or sort the list as per your criteria.
More information can be found in this blog post.