Hello @myominkhaing02, sorry for the long reply.

1. For items with the Valuation Method = Average, it's possible to create an IN Adjustment document without specifying the qty on the document. And the Average cost will be used in all IN Issue documents with the item.
2. At the same time in IN Receipts, the system will default either the Last or Average Cost depending on the Avg. Default Returns Cost value option defined for a specific warehouse: For example, if the Avg. Default Returns Cost = Last, the Last Cost value will be automatically populated in IN Receipts.

Hi @Irina 
Thank you for this answer.
Could you please elaborate briefly on option 1. 

Maybe you could provide a screenshot, where IN303000 is properly filled in order to be used on all existing qty’s of an item. 

Thank you!