Problems logging in after changing WordPress address URL

I was helping a friend with their website the other day which they access online, with apparently no downloaded software. It appears that their login details are purely for their website as the user name is ADMIN !!!

They were trying to port their site to a new domain name, and changed the Site address and WordPress address under general settings.

They had obviously done it wrong because it immediately displayed their new domain page (advert) without the wordpress content.

To try and correct that we have put a forward on their new domain (www.bbb.com) so it pushes back to their original site (www.aaa.com) from there they can add //wp-login.php and get to the WP login, but when they enter name and password it fails to do anything because it is obviously sending the detail to (www.bbb.com) and finding no WP.

Is there a fix to get back to the dashboard so that we can remove the offending forward?