Hi,
You can not cancel GI.
If you are using FIFO, then you can not change the price when making GI, because system calculates price by FIFO.
You can do one thing, use Inventory -> Inventory Transaction -> Inventory Revaluation
Here you can change Item price of any transaction, enter Itemcode, it will show the transactions of which stock is currently available. You change the rate in GR as per GI. Accouting effects will be posted correctly.
This is the wayout to match the prices.
Regards,
Amrut Sabnis