Temp site but WP forwards to real domain

I installed WP on a temporary host and it’s running fine, but then I when I was editing the information about the site, I forgot and entered the permanent domain name and now when I try to log into the admin pages, I get redirected to the permanent domain (which doesn’t have WP installed).

I know there’s a file I can edit using FTP to change the domain back to the temporary address, but I can’t remember which one it is. Anyone know the name and directory?

Thanks,

Lee