How to merge last commit with one before

It could be useful if you for example forget to update version number along with main changes.

git reset --soft "HEAD^"
git commit --amend

You will have a commit with a name of one before the last one.

You can merge as many commits as you want, as long as they are the last X commits, and not somewhere in the middle. Just run git reset --soft HEAD~N, where N is the number of commits you want to merge.