First, make sure your repo is up-to-date with "git fetch." This will pull down the tag you made, including the wrong one.
Next, delete the old tag by running:
git tag -d [tag-name-here]
So, for example, I did:
git tag -d v1.1.0
Next, commit and push your latest changes including the change you want the release to point to:
git add folder/file
git commit -m "message here"
git push -u origin master
Finally, push your tag changes as well:
git push origin :[tag-name-here]
If your tag has the same name as a branch, run:
git push origin :refs/tags/[tag-name-here]
Now, open GitHub in your browser and navigate to the "releases" page. Your release should now be listed as a "Draft" because its tag has been deleted.
You can now discard this release and create a new one with the same name pointed at the most recent commit.