I have performed the following merge:
A---B---C---E (HEAD, merge of C and D)
/
D---|
But I noticed some issues in E, and fixed them in F:
A---B---C---E---F (HEAD)
/
D---|
I want to modify commit E so that it contains the "fixup" changes made in F.
When I try git rebase -p -i HEAD~2, it tries to create a regular (not merge) commit, and even tries to make me re-resolve the conflicts I already resolved when performing the merge for E.
How do I fixup commit E so it contains the changes made in F?
git reset --soft E
git commit --amend
should be enough. It'll recreate a merge commit (with a different hash than E, let's call it E') while inserting whatever changes you made between E and F.