Uhm, I do a lot of git rebase -i HEAD~2 where I just squash the commit on the latest or sometimes I need to reorder and move the fix commits in specific commits in Pars that multiple commits, which I then need to push force. Is this for a similar use-case? I am not familiar with fixup or how it works.
fixup lets you mark a change to be rolled back into a previous commit, without changing the history (yet). When you do `git rebase --autosquash` it then automatically moves those commits as `fixup` in the right places. It helps to queue up many fixups at once and only have a single rebase to do when you're done (or for reviewers to see just the changes in a review tool, not have to reassess the entire commit because you already rebased)
btw you could be doing `git commit --amend` if you just want to add to the last commit.