How can I move a tag on a git branch to a different commit?

I created a tag on the master branch called v0.1 like this:

git tag -a v0.1

But then I realized there were still some changes I needed to merge into master for release 0.1, so I did that. But now my v0.1 tag is stuck on (to invoke the post-it note analogy) the wrong commit. I want it to be stuck on the most recent commit on master, but instead it is stuck on the second most recent commit on master.

How can I move it to the most recent commit on master?