git reset filename

$ git status
On branch master
Untracked files:
(use "git add …" to include in what will be committed)

another_file.html

nothing added to commit but untracked files present (use "git add" to track)

barzik@BARZIK2 MINGW64 ~/test/examplegit (master)
$ git add another_file.html

barzik@BARZIK2 MINGW64 ~/test/examplegit (master)
$ git status
On branch master
Changes to be committed:
(use "git reset HEAD …" to unstage)

new file: another_file.html

barzik@BARZIK2 MINGW64 ~/test/examplegit (master)
$ git reset another_file.html

barzik@BARZIK2 MINGW64 ~/test/examplegit (master)
$ git status
On branch master
Untracked files:
(use "git add …" to include in what will be committed)

another_file.html

nothing added to commit but untracked files present (use "git add" to track)

barzik@BARZIK2 MINGW64 ~/test/examplegit (master)