If your original seller details are nowhere to be found, then yes you will have to start all over. But I would create a test set first, as described above, just to make sure you know you can do it successfully, with a minimum of work. The saved seller details will be found by clicking "Manage Seller Details". Give it a try, don't forget to SAVE. If it doesn't work, file a support request and support staff will give it a go. You might want to review the tutorials on this as well.