How to Reverse a Clear Manually entry

We wrote a check before receiving the invoice. The invoice was received and entered.  The check was applied against the invoice in the clear manually area of Payables.  The check was returned from the supplier and we need to void the check.  SAP will not allow this because it has already been applied to the invoice. How do I reverse the clear manually entry to get both the check and invoice open in SAP.  How do I apply a check to an invoice and still leave the check as uncashed for future applications.

Thanks,

Rose