How to "Un-push" a file in git?

WARNING: Since you mentioned a pull request I am assuming that you are pushing to a separate branch that nobody else is working on other than you. Otherwise, doing a force push is usually discouraged.

Let's assume some state:

$ touch fileA.py fileB.py fileC.py
$ git add .
$ git commit -m "my message"
$ git push

$ ls
fileA.py*  fileB.py*  fileC.py*  

$ git ll
* 537443d - (HEAD -> my-branch) my message (9 seconds ago) <Aleksander Stelmaczonek>
  0     0       fileA.py
  0     0       fileB.py
  0     0       fileC.py  

Note: git ll is my custom command alias, see the definition at the end.

To remove the fileC.py from the commit and yet leave it in the working dir you can use git rm command and then amend your commit and re-push it (force push) replacing the original commit with an ammended one. Please, note that by default this command also removes the file from the disk and you need to use --cached option.

$ git rm -h
usage: git rm [<options>] [--] <file>...

    -n, --dry-run         dry run
    -q, --quiet           do not list removed files
    --cached              only remove from the index
    -f, --force           override the up-to-date check
    -r                    allow recursive removal
    --ignore-unmatch      exit with a zero status even if nothing matched

Now:

$ git rm --cached fileC.py
rm 'fileC.py'

$ git status
On branch my-branch
Changes to be committed:
        deleted:    fileC.py

Untracked files:
        fileC.py

$ git commit --amend -m "my message"
[my-branch beebdc1] my message
 Author: Aleksander Stelmaczonek <Olek@TPOLEK.localdomain>
 Date: Wed Nov 10 18:25:37 2021 +0100
 2 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 fileA.py
 create mode 100644 fileB.py

$ git ll
941acb2 - (HEAD -> my-branch) my message (13 seconds ago) <Aleksander Stelmaczonek>
  0     0       fileA.py
  0     0       fileB.py

$ ls
fileA.py*  fileB.py*  fileC.py*

$ git push --force

I would like to strongly emphasize that doing a force push is a really bad idea if there is more than one person working on this branch. Potential issues are not so easy to resolve, especially for a novice.

Generally speaking, I highly recommend reading the Git Book. It's free and well written. For novices, worth reading are chapters 1, 2, 3, 7.1, 7.2, 7.3, and 7.7.

Personally, for all stuff related to creating and modifying commits I usually just use a GUI. Find out what GUI tool suits you best. I use https://git-fork.com/.

This is how you can enhance your git experience with my git ll command (and others):

git config --global alias.ll "log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %Cblue<%an>%Creset' --abbrev-commit --date=relative --numstat"

In Git, the equivalent of "unpush" would be to force push what was there before your push. Whether or not you should force push depends on a few factors, the primary one being if others might be building off of the version of your branch that you already pushed. Generally in public repos force push is frowned upon, and in private repos it's frowned upon on shared branches (such as main, master, develop, etc.)

That being said, in your case, it sounds like you don't really want to "unpush", but instead, "push something else" (which also requires a force push).

If you currently have your branch checked out, and you are at the place where you just made your one commit, and if it is OK to re-write your branch because no one else is using it, then this should achieve what you want:

git reset --mixed @~1 # Go back to the previous commit; leave files alone
git add FileA.py FileB.py # Stage only the files you want to commit.
git commit -m "Add files for new thing"
git push --force-with-lease # Using --force-with-lease is usually best practice

Note in the first line --mixed is redundant since the default reset is mixed. That line could instead be git reset @~1. I left it in so it's clearer from a learning standpoint since you are new to Git.

Alternative: if the conditions are such that you can't (or shouldn't) force push your branch, then instead you can either:

1. Create a new commit by reverting the previous commit, and then re-create your new proper commit, and push those 2 commits out.
2. Add one more commit to delete the file you don't want, and then push that out.

Sounds like you want to replace the pushed commit. (Rewriting history like this is not advised in a multi-user setting.)

First, revert to before the commit

git reset HEAD^

Then recreate the commit and push the new commit. You will need to use force.

git push --force-with-lease   # A safer version of -f/--force

Before you start, you should tag the problem commit.

git tag bad

This allows you to easily restore the original state if anything goes wrong.

git checkout mybranch   # In case you changed away
git reset --hard bad