I am curious about how to remove the first commit in git.
What is the revision before committing any thing? Does this revision has a name or tag?
For me, the most secure way is to use the
git update-ref -d HEAD
It will delete the named reference
HEAD, so it will reset (softly, you will not lose your work) all your commits of your current branch.
If what you want is to merge the first with the second one, you can use the
git rebase -i --root
A last way could be to create an orphan branch, a branch with the same content but without any commit history, and commit your new content on it:
git checkout --orphan <new-branch-name>