accident on 'general' page creates redirect; inhibits access to wp backend

I am building a site under a different url than what it will be released under. On the ‘general’ setup page, at the top, by mistake, I typed in the actual url that it will be running under later. Now I can not get into backend for the site because it redirects to existing site (which will be updated with my new site when I’m done). How do I get back in?