Hi,
Cancel the payment document for vendor 1st and then cancel invoice followed by GR document. Refer
GR/SES reversal after invoice payment
Once all documents reversed, you can set deletion flag to the line item in PO and enter new line item by entering correct project details, then carry out GR, Invoice and payment for vendor.
NOTE:
Also cross check FI/CO team - can you transfer project value with cost object related to new required cost object to ignore above said process.
Regards,
Biju K