How do I add a discount after a item has been fulfilled?

[marine2231]

I fulfilled an order without realizing I needed to apply a 20% discount.  How do I do that after the order has been placed and fulfilled? This is a net30 order so I haven't collected payment - just fulfilled. 

Please help! 

Thanks in advance

[CrazyDoubleJ]

I got the same requirement.

[SchoppeeFarm]

I also have the same problem and there does not appear to be a solution other than cancelling the order and creating a new one. 

[kickinyourcup]

I have the same question...