You should be able to take care of this yourself. Click this:
https://groups.google.com/g/video-downloadhelper-q-and-a/c/BzPLK2YyL-s
You'll probably want to bookmark that one for easy reference. I recommend you read that
entire thread, if not now, eventually. As you read through that you'll come across a
reference to what to do if you've lost your license. You can skip quickly to the
relevant reference by doing a string search on "lost" in there. That will reposition the
web page to the right reference. There is a link there that you should click. That
should fix you up.
There is another discussion in that thread that is likely going to come in handy for you.
You can find it quickly by doing a string search on "revalidate" in there. You'll find
instructions for what to do if your license becomes locked & needs to be revalidated.
Good luck!