Wrote the wrong thing in your commit message?
If you need to make multi line changes its better to use this command because it will open the editor:
git commit --amend
For a quick edit its easier to use the
git commit --amend -m "New commit message"
Careful with any staged changes you have, they will be committed when you amend your commit.
If you need to edit the message of a commit already in your remote branch, you'll have to force push your changes.
git push <remote> <branch> -f