git stash -u
Stash files included the untracked ones
git log --full-history --all -- <path-to-file>
git log -u <path-to-file>
Search in all commits that touch the file (the second command shows up all the differences)
git fixup <hash_of_commit>
Create a fixup commit
git rebase -i --autosquash <hash_of_commit>
Squash all fixup commits and rebase in the hash one