how to add expense account on an inventory item? there is a income ,COGS and asset account. The problem is when we enter a vendorbill with an inventory item , the asset account is used but how to impact an expense account?

You need to use different type of item like non inventory or services item. Inventory normally have cogs account only.

but when you impact the expense account ? if I use a stock change account as an asset account , the gl impact is like you say But it’s not an expense