We've added an amend link, that should take you right where you need to go.
Once you click through here, you will need to click the "edit" button that is adjacent to the "Attendee 1" field. This should take you back into the registration details pages. You shouldn't have to change any of your info, but you will need to click "Proceed" on 3 pages before you see the workshop options. Select the workshops you want to add, and then you should proceed as normal to the checkout.
Hope this helps!
