BoM Cost update

Hi

I issue with BoM unit cost which is inflating the item cost price. User by mistake posted wrong quantity and hence wrong unit price for an item on purchase invoice. This item is used in BoM for many other manufactured. The error was detected yesterday while looking at COGS. All the items on BoM using this raw material is showing unit cost of £0.45 instead of £0.04. We have rectifed the item itself by issuing credit note and then reentering the invoice with correct quantity & unit cost. My BoM is made of 3 tiers. First and item is made from raw material, then it is packed in packs of different size. Now at this second level, the item (bags) is showing correct cost of £0.04 after correcting the purchase invoice but on the 3 tier where each small packs are packed in 1 box of 12 such packs, the cost of single pack is automatically corrected. It is still showing old unit cost. I want to update unit cost to the actual cost. I know there is no cost update procedure in FA. So how do I fix this?

Thanks