To open a previously invoiced or closed Work Order, you'll have to reverse either of these processes, depending on the case at hand.
1. Go to Work Order.
2. Click on the three-dot menu next to the invoiced or closed Work Order.
3. Select the "Reverse Invoice" or "Reverse" option.
Then, you can make the changes, and reinvoice if desired.
*Notice that when reinvoicing, you can assign the same invoice number and date.