After you perform a commit while global git config is not set, you can set the author without editing the commit.
git config --global user.name "Your Name"
git config --global user.email "you@example.com"
git commit --amend --reset-author --no-edit--amend creates a new commit that will replace your existing commit
--reset-author updates author/committer with the current config
--no-edit retains original commit message