The most common meaning of “revert” is “to return to an earlier condition, time, or subject.” When Dr. Jekyll drank the potion he reverted to the brutish behavior of Mr. Hyde. But in South Asia it has become common to use “revert” instead of “reply,” writing when people want you to get back to them about something: “revert to me at this address.” In standard English this would literally mean they are asking you to become them, so it is best to stick with “reply” when dealing with non-South Asian correspondents. Even some South Asians disapprove of this use of “revert.”
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