Incorrect Domain Name Entered – Now Can't Access Site

My son made some revisions to my website this evening but stupidly he changed the website URL setting in the Dashboard from the original and correct one to a new domain name that has recently been purchased but as yet has no hosting attached to it.
Obviously as the Dashboard thinks the URL for the site has changed I can no longer access either the site or Dashboard to make the corrections. I have looked in cPanel (domain is through GoDaddy) but cannot find any file that seems to relate to the URL input.
Help would be much appreciated as I’m at a loss as to what to do and I know my son is feeling very guilty.