This question already has an answer here:
When I visit recently-active but old questions, I often find that the activity consists of a new answer which duplicates, in briefer form, a long-existing answer. Such answers are often from new users and are generally reasonably accurate, but entirely duplicative of another answer long since posted.
What should I do in this case, as a <10k user?
Should I downvote it? Should I flag it? Should I comment on it?