None of these answers with the use of HEAD@{1}
worked out for me, so here's my solution:
git reflog
d0c9f22 HEAD@{0}: commit (amend): [Feature] - ABC Commit Description
c296452 HEAD@{1}: commit: [Feature] - ABC Commit Description
git reset --soft c296452
Your staging environment will now contain all of the changes that you accidentally merged with the c296452 commit.