If a commit message contains unclear, incorrect, or sensitive information, you can fix it locally and push a new commit with a new message to GitHub.

Commit has not been pushed online

If the commit only exists in your local repository and has not been pushed to GitHub, you can amend the commit message with the git commit --amend command.

• On the command line, navigate to the repository that contains the commit you want to amend.

• Type git commit --amend and press Enter.

• In your text editor, edit the commit message and save the commit.

The new commit and message will appear on GitHub the next time you push.

Amending the message of the most recently pushed commit

• Follow the steps above to amend the commit message.

• Use the push --force command to force push over the old commit.

git push --force example-branch

Source