Add new file to commit

You should use the parameter --amend , if the last commit

git commit --amend
git add file2.txt

And when using push:

git push --force <repository> <branch>

  

Reference:    link

If you make --force , and other authors have created new commits however, those commits will be permanently deleted . --force is recipe for disaster and should be avoided at all costs.

--amend is recommended only if the commit has not yet been published.

As in this case the commit has already been published, it is best to create a new commit with the new files. amend is rewriting history, it's lying to git .