Just intimate your jurisdictional range superintendent along with the details that you have by oversight passed on excess excise duty which received from the manufacturer.
Also mention this that you are re-crediting the excise duty excess passed on to your customer and issuing the credit note to your customer.
After that you will issue an invoice to original manufacturer debiting re-credit amount of excess duty. Now your RG23 D register will show nil impact.
On the basis of invoice issued by you the original manufacturer will take cenvat of excise duty paid in excess.