Hi Gayle_Clarke welcome to the GoTo Community.
The registrant is seeing the BST timezone based on their web browser settings and calendar app settings.
So once you schedule a webinar in your timezone, when the attendee clicks the Registration link and lands on the Registration page, GoTo Webinar will detect which timezone they are in (based on their web browser settings) and automatically adjust the date/time. When they add the session to their Calendar app by downloading the .ICS file their email client will automatically adjust the date/time based on their Calendar app's settings.
