How to undo the most recent commits in Git

$ git commit -m "Something terribly misguided"              (1)
$ git reset HEAD~                                           (2)
<< edit files as necessary >>                               (3)
$ git add ...                                               (4)
$ git commit -c ORIG_HEAD                                   (5)

1. This is what you want to undo
2. This leaves your working tree (the state of your files on disk) unchanged but undoes the commit and leaves the changes you committed unstaged (so they'll appear as "Changes not staged for commit" in git status, and you'll need to add them again before committing). If you only want to add more changes to the previous commit, or change the commit message¹, you could use git reset --soft HEAD~ instead, which is like git reset HEAD~ (where HEAD~ is the same as HEAD~1) but leaves your existing changes staged.
3. Make corrections to working tree files.
4. git add anything that you want to include in your new commit.
5. Commit the changes, reusing the old commit message. reset copied the old head to .git/ORIG_HEAD; commit with -c ORIG_HEAD will open an editor, which initially contains the log message from the old commit and allows you to edit it. If you do not need to edit the message, you could use the -C option.

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¹ Note, however, that you don't need to reset to an earlier commit if you just made a mistake in your commit message. The easier option is to git reset (to upstage any changes you've made since) and then git commit --amend, which will open your default commit message editor pre-populated with the last commit message.
Beware however that if you have added any new changes to the index, using commit --amend will add them to your previous commit.
---- Edit by Frank R. 2018-3-9
If pushed,

git push origin master --force

Gitlab - Command line instructions

Git global setup

git config --global user.name "Nguyễn Văn Hưng"
git config --global user.email "hungnv@runsystem.net"

Create a new repository

git clone git@gitlab.com:hungnv-runsystem-net/test.git
cd test
touch README.md
git add README.md
git commit -m "add README"
git push -u origin master

Existing folder

cd existing_folder
git init
git remote add origin git@gitlab.com:hungnv-runsystem-net/test.git
git add .
git commit -m "Initial commit"
git push -u origin master

Existing Git repository

cd existing_repo
git remote rename origin old-origin
git remote add origin git@gitlab.com:hungnv-runsystem-net/test.git
git push -u origin --all
git push -u origin --tags