General Ledger accounts are created in QuickBooks Online by going to Settings > Chart of Accounts
Next you will click New
The Cost of Goods Sold account set up would generally look as follows. The Account Type is Cost of Goods Sold. The Detail Type is Supplies and Materials COGS. The Name can be anything you would like to assign.
The Inventory Asset account set up would generally look as follows. The Account Type is Other Current Assets. The Detail Type is Inventory. The Name can be anything you would like to assign.
Once you have created the necessary accounts you need in QuickBooks then you can return to A2X. For A2X to be able to see the new accounts in the Costs Settings page you will need to go to A2X Settings > Connections and click the Refresh QuickBooks Cache button.