The exclusion of up to $5,000 for death benefits no longer applies. It had applied only for employees who died before August 21, 1996. Only a death gratuity paid to a survivor of a member of the Armed Forces continues to be excludable from gross income.
On Form 1040X, you may file an amended return within a three-year period to claim a refund or correct a mistake made on an original or previously amended return.