"Black adder" edited my answer to a question asking for a proof of noether normalization. the edit was nicely done, except in the next to last sentence a change was made from "≤ d" to "less than d", which introduces an error. I do not know how to either fix it or message the editor of the question. Or perhaps, in some languages "less than" means ≤?
To make a minor fix to an edit that took effect one proceeds as for a general edit of the post, that is one selects "edit" just below the post, makes the necessary change, and saves it.
It is possible to message editors of a post using the usual @user-syntax for comments; that is one writes a comment starting (or at least containing) @username where username is the the editor's displayname (without space). In fact, it suffices to use the first three (or more) characters too, but it needs to be the start of the displayname, so I could notify you with @roy or @roysmith or @roysm yet not with @smith).
For completeness let me add it is also possible to undo an edit completely. To this end go to the revision history of the post (clicking the timestamp in the middle at the end of the post; note if the post was not edited it is not there so for example on this meta post it is not present [indeed on your meta-post it is meanwhile present]). There you see all old versions. Look for the one you want to go to and click "rollback" there.