How do I undo a part of the changes applied to a file that happened a while ago. I have the following commits and the accidental changes happened between A and B to file.txt:

...--A--B--...

I have a diff patch of the file in file.txt-B-A.patch which reverts all changes. However I only want to undo certain changes in file.txt, much like manually picking changes in a merge conflict. Is there a way to do so without modifying the patch file?

git merge undo
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