The freight cost already posted in FI account with MIGO.
Better you cancel the MIGO.
If you stock is not exists in plant sloc,
Than first do 561 on this plant ans storage location as on MIGO date, and note down the material document number.
Now you can able to cancel the goods receipt..
Cancel the goods receipt. Then correct the freight amount on PO, then again do MIGO.
When the MIGO is done into this plant and storage location, then cancel the 561 material document.