Is it possible to delete all “new cards” in my deck, cards that I have not seen yet? I have happened to duplicate all the cards…
I just want to practice on those cards I have already gone through and delete those I have not seen.
would have been very grateful if someone answered! 
Hi!
If you got an up-to-date version of Anki (2.1.41+), you should find various filters on the sidebar. There is a filter for new cards as well:
Select your deck on the sidebar, then hold ⌘ (or Ctrl on Windows) and click the “New” filter highlighted in the image above.
A search for new cards within your deck should then be triggered. It should look like this:
If you are happy with the search result, select one of the notes, hit ⌘/Ctrl + A to select all of them and right click → delete.