Hi i am new to nav i need some suggestions,

In sales order while we post prepayment a multiple invoices will hit and once after post credit memo all invoices will get reverse for a particular sales order instead of that i need to select a particular invoices and post the credit memo that particular invoice amount only want to get reverse. 

For that i have one action button on that posted sales invoices for doing this concept

I need some suggestions based on this..

 Thanks in advance,