Once the judges have been invited, you can start assigning them to the Eligible submissions (even if they haven't accepted the invitation yet). If submissions are still in "Not Verified" status, you won't be able to make assignments. Make sure you've marked the ones you would like evaluated by the judging panel as "Eligible" first.
Next you'll have the option to either manually assign judges to each submission, or randomly assign judges to all of them at once.