From a month, a lot of people are facing this problem. There is a option to delete your current url and set a new one. But if we click on that then it shows YouTube is currently updating their system. For this reason we cannot change our url.
You can't fix this problem. But all you can do, give feedback to teamYouTube and wait for more few days.
It is a short solution. Don't try to find another way. Because it't the only one way.
