How can I change the Unit Cost?

How can I change the Unit Cost on an item that has QOH=0.  The average cost is being calculated at 330.25 whereas the actual cost is .04 per unit.  There was a huge error in purchase receipts.

I did a spreadsheet that shows all of the entries done.  This spreadsheet shows that we had 500 units and the total cost amount from value entry was $165121.8254 giving us an average cost of $330.24366.  We did an entry to take out this inventory - -500 @ $330.24366.  Now the spreadsheet says we have 0 quantity and 0 costs.  The Item Card says we have 0 quantity at Unit Cost of $330.24366.  Will that change automatically when we purchase more at .04?  

The problem is that the wrong cost comes up when doing estimates.  Is there a way to change the Unit Cost when QOH is zero?