How to Use Git's `splitnew` Command to Split a Commit into Two Separate Commits

`splitnew` is a command in Git that allows you to split a commit into two separate commits. It is used when you want to undo some changes made in a commit, but keep the changes made after that commit.

Here's how you can use `splitnew`:

1. First, find the commit that you want to split. You can do this by using `git log` or `gitk --all`.
2. Use `git splitnew` with the commit hash of the commit you want to split. For example:
```
git splitnew 0123456789abcdef
```
This will create a new commit with the changes made after the commit you specified, and undo the changes made before that commit.
3. If you want to keep the original commit message, you can use the `--keep-message` option. For example:
```
git splitnew --keep-message 0123456789abcdef
```
This will create a new commit with the same message as the original commit.
4. If you want to squash the original commit into the new commit, you can use the `--squash` option. For example:
```
git splitnew --squash 0123456789abcdef
```
This will create a new commit that combines the changes made before and after the specified commit.

Note that `splitnew` is a relatively new command in Git, so it may not be available in all versions of Git. If you're using an older version of Git, you may need to use a different command, such as `git reset` with the `--soft` option, to achieve similar results.