To clarify, in the "Get a customURL" box, you'll see the customURL(s) you've been approved for. You can't change the part in the gray box, but you may need to add a few letters or numbers to make the URL unique to you. Hope this info helps.
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more