Given you have a patch that doesn't apply to the current HEAD, but you know it applied to some commit in the past, git rebase-patch will help you find that commit and do a rebase.

Usage: git rebase-patch <patch-file.patch>

(Note: If the patch has been created with git format-patch, it is more efficient to use git am, because that considers meta information from the patch.)

You can reroll a patch against the current HEAD like this:

git rebase-patch old-patch.patch

That might give you:

Trying to find a commit the patch applies to...
Patch applied to 9d1a78c as 9e22d99
[master 4d28217] remove-second-paragraph.patch
 1 file changed, 2 deletions(-)

Now your latest commit has the changes of your path. It's message is the patch file name. Then proceed as usual.

Reroll the patch:

git diff HEAD~1 > new-patch.patch

Change the commit message:

git commit --amend