There is a procedure: flag the answer so a moderator can take action if it's needed.
In addition, you can:
- downvote the answer
- post a comment to politely point to the copy-paste and explain that this is not an encouraged behaviour.
And of course, if another answer is suitable, there is a chance that the question is a duplicate too, so you can vote to close it if warranted.
all joking aside...
There are three scenarios I can think of
1 (one). Answers are trivial and therefore similar
2 (two). Answer is a dupe of the same user's answer
3 (three). Answer is copied directly from another user
If the answer is somewhat similar (as often happens with questions whose answers are trivial), please don't worry about it. We have lots of users who obsess about this. "His answer for a regex that matches all words with more than five letters is exactly the same as mine!" Well, no offal, Sherlock. In cases like this, just move on (preferrably), downvote (not even worth it), or move on. Or you could just move on. Moving on is best.
If the answer is an exact copy of another answer by the same user, don't worry about it. The website will automatically flag these for moderator attention.
If, as in this case, the answer was a direct copy of another users' work, PLEASE flag it for moderator attention! That is unethical and an abuse of our users, and will not be tolerated.