How to undo the last commit in git

Try simply to reset last commit using --soft flag

git reset --soft HEAD~1

Note :

For Windows, wrap the HEAD parts in quotes like git reset --soft "HEAD~1"

I think you haven't messed up yet. Try:

git reset HEAD^

This will bring the dir to state before you've made the commit, HEAD^ means the parent of the current commit (the one you don't want anymore), while keeping changes from it (unstaged).