Expense Refund Process?

Hi - I have a query about Expenses on 22A.

An Expense Claim was approved and interfaced to AP and the invoice has been paid to the member of staff.

However - it should not have been as the mileage claim was claimed from home and not the office base.

What process should be followed to retrieve the costs already paid to the employee?

Does anyone know? Sorry this is a basic question.

Any advice much appreciated.

Thanks