Budget Check Error due to incorrect BUDGET_REF

Hi. An accountant issued an invoice by copying an existing invoice. It had a budget check error due to an incorrect BUDET_REF. The accountant corrected the BUDGET_REF and the invoice budget checked successfully. When the account then had to issue the credit invoice, the BUDGET_REF was again set to the incorrect value. However, the accountant is unable to change the value and the invoice will not budget check. What would be the best way to override the BUDGET_REF so that the invoice will budget check?