Here is a shortcut to correct all the commits of a branch and set them to a specific user name and user email. This does not correct commit messages in themselves. Replace $USER_NAME by the user name and $USER_EMAIL by the email wanted.
git filter-branch --env-filter 'export GIT_AUTHOR_EMAIL="$USER_EMAIL";GIT_AUTHOR_NAME="$USER_NAME"'
This command checks the author name and email and rewrites all the commits one-by-one. Current branch be rewritten with new data so may differ from a remote branch.