Change Author of Commit N

example:
want to change commit hash in remote: 12345678

locally in your pulled repo. you are on the master branch, run the following:
git checkout 12345678
git commit --amend --author "AUTHOR_NAME <AUTHOR_EMAIL>"
   ==> get the commit hash printed after you run this (i.e. 87654321)
git replace 12345678 87654321
git filter-branch -f -- --all
git replace -d 12345678
git push -f origin master
git checkout master