How do I contact the poster of a deleted answer?

Poster A gave an upvoted and accepted answer to a question. Poster B also answered the question, but then deleted his answer—perhaps after a quick glance at A's short and simple answer, considering that his own was no improvement. However, A's answer was wrong while B's (deleted) answer was right. I would like to point this out to B. How can I do this?

• Unfortunately there is no response from A, B, or the OP. The question is like "what is the sum of $2$ and $2$"? Poster A answers $5$, an answer which is upvoted by viewers and accepted by the (transient) OP. If someone then edits A's answer, changing the $5$ to $4$, it is no longer the answer that A gave nor the answer that bore the upvotes and acceptance. So I won't do that. What I have done put up my own answer ($4$). Nov 15 '19 at 13:15