I've discovered a work around. Maybe some others have already discovered this too.
It is very clumsy, but seems to work.
Assuming you have a backorder that hasn't failed yet, click on the change settings link.
In a different window, click on a backorder that has failed, and copy the 6 digit MonitorID= number.
Change the MonitorID number on the live backorder for the MonitorID that you want to change and hit return.
This then gives you a page where you can change the failed backorder.
It seems to work for me, but if anyone has difficulties with this method, you might like to post here.
Make sure you don't make a mistake and replace the wrong backorder by mistake though!
It would of course be a *lot* easier if godaddy fixed their site.