Wordpress 5.3.2    CiviCRM 5.21.0

I've recently upgraded to CiviCRM 5.21.0 successfully and everything was working fine. 

Whilst tidying up the site, I inadvertently and stupidly changed the CiviCRM Resource URL to the site URL (not the full path) instead of [civicrm.root]/
I now cannot get into CiviCRM admin through Wordpress admin so am unable to change the resource URL back to how it was.

Does anyone know a way of resettting things through FTP or phpMyAdmin please?

The settings in civicrm-settings.php seem OK.

Many thanks.