RMA Tax reversal Reversal

Hi,

Created a Sales Order with Excise tax.

AR Invoice is generated with Tax amount.

RMA created refering the Original sales Order.

While making the receipt, User forget to process IL Taxes.

Auto Invoice run for the RMA

Credit memo created for the RMA.

Now in the tax amount is pending in the Original Invoice.

How to reverse the Tax part so that the balance amount in the Original AR Invoice become Zero.

Regards