This is a scenario I've run into multiple times: suppose you have a feature branch, and you then need to merge in the develop branch and resolve conflicts prior to your PR being merged. You merge develop, fix all the conflicts, run and test your code, and find you made one very small mistake in fixing the merge conflicts. You make one small commit fixing that incorrect merge conflict resolution. Now, you want to clean things up and squash this last commit into the previous commit, which is a merge commit. Is there any way to do this without having to manually redo all of your merge conflict resolution?
If you just committed your last fix commit that you talked about, you can do this:
git reset --soft HEAD~ # keep the pigtail
git commit --amend --no-edit
Voilá!