Assign the requirement to the iteration you created, update
Set the estimate to zero, update
The requirement remains assigned to the iteration with an estimate of zero, and the iteration input is disabled. I'm not sure what should happen when you set the estimate to zero. Maybe that should be disallowed and you are forced to move the requirement to the backlog first, or maybe it should move to the backlog for you.
The requirement remains assigned to the iteration with an estimate of zero, and the iteration input is disabled. I'm not sure what should happen when you set the estimate to zero. Maybe that should be disallowed and you are forced to move the requirement to the backlog first, or maybe it should move to the backlog for you.