Changed Site URL / Site Address in Settings-General by Mistake

Hi!

I just installed WP on my site, www.sample.com, and I also created a subdomain, www.sub.sample.com. Both have separate WP installations. What I was trying to do was use a page as a homepage and the blog itself in a subdirectory–which I know now how to do. By mistake and confusion, in Settings->General, in the Site URL / Site Address section, I put www.sub.mydomain.com in one of the boxes and www.sample.comin the other. (I forgot which is which.)

What happens now is when I login to www.sample.com, I am taken to the login screen of the www.sub.sample.com. And when I login there I go back to www.sample.com, and vice versa.

Is there a way to fix this? Thanks!