Refund for customer

Hello, the customer has paid the highest amount by bank transaction. We need to return to the same account we received
so please give me sugestion how to handle this situation

have you read the guide on refund to customer?

when need to refund full invice amount i understand well but partial payment pls me explain

the guide does not mention anything about full invoice refund. the process is same as explained in the guide irrespective of the amounts.
did you read the guide as suggested earlier?

Pay a refund