Unfortunately, there is no way to update the valuation method of an item while it’s in stock. Similar to a couple of other issues here related to changing base unit of measure:
and here:
You cannot edit certain settings on a item while you have it in Stock. To update your valuation method, you’ll need to do the following steps (we did the same thing for a client back in July). Before you start, make sure you have no open shipments/SO Invoices and receipts/PO Bills or other inventory allocations. Here’s what we did for our client.
a. Prepare an Inventory Issue transaction to remove all impacted inventory from Acumatica at its current cost, regardless of what that cost may be.
b. Validate that the inventory balance for impacted items is 0 qty and $0.
c. Prepare and run an import scenario to change all Stock Items from Standard Cost to Average cost.
d. Verify that all items now have Average Valuation.
e. Using the same data as the Inventory Issue, prepare an Inventory Receipt to add back all inventory to Acumatica to the same accounts and locations that it was removed from at the same prices it was removed at. (Or, if you are changing the actual $ value of your items then update accordingly and with the right reason codes to account for the cost variances)
f. Verify that the inventory quantity and valuation match the original amounts.
g. Update Item Classes for Stock Items to ensure all new items created in the future have “average” valuation.