Leave your original invoice(s) and payment(s) intact for tax and historical purposes. Changing these will usually mess up your end of day cash transactions report.
They need not be touched to properly handle an NSF payment
Steps
There are two options
Option 1.
Make a new A type invoice for the NSF customer.
Using the drop down menu to the right of the Add Item icon, add the G/L code to the invoice for your bank, usually 1010
Use a quantity of one, and the amount equal to the NSF unpaid balance.
Add a comment to the invoice line Description explaining why it was created and by whom, etc.
Option 2.
Create a Non Inventory Type Category in Category Maintenance called NSF Payments
Set both of the Income and Cost ledger numbers for that category to your Bank Ledger or NSF Ledger account number if preferred
Add a Part to the NSF Category called NSF Fee or Returned Item, no other details are needed
Make an A invoice to that customer, sell the NSF Part wit a quantity of one, and the price equal to the NSF unpaid balance.
Add a comment to the invoice line Description explaining why it was created and by whom, etc.
The above does the following for you:
Put the amount of the NSF check back onto the customer as an A/R balance
Removes the amount of the NSF from the affected bank account.
Leaves an invoice we can accept a replacement payment against to settle the debt (or worse case eventually write off as bad debt).
Keeps a historical trail for future reporting.