While building some shelves in my basement, I noticed an electrical cable than ran along a joist and dead-ended. I tested it and discovered it didn't have power. As the dead-end is not particularly far from the breaker box (~20 ft of cable), I'd like to remove it entirely just to be tidy.
I haven't yet removed the front panel of the break box to investigate because I wanted to do some reading first to make sure I feel comfortable doing so. I see plenty of articles and videos on how to replace circuit breakers (though I don't believe I want to replace or even remove any existing breakers).
However, what I do not see in those articles is what I should do to the breaker box after removing the cable. I assume I should replace the knock-out so that there isn't a hole in the side? Is there a recommended way to do so? Anything else I should do? Apologies that this is likely a very simple question - I'm just not sure on the terminology of what I should be searching for.
In the photo below, the cable I wish to remove is in the second black hole from the bottom (just above the yellow cable).