The following is from the IRS instructions for Form 1040X, page 3.
Deceased taxpayer. If filing Form 1040X for a deceased taxpayer, enter “Deceased,” the deceased taxpayer's name, and the date of death across the top of Form 1040X, page 1.
If you are filing a joint return as a surviving spouse, enter “Filing as surviving spouse” in the area where you sign the return. If someone else is the personal representative, he or she must also sign.
Claiming a refund for a deceased taxpayer. If you are filing a joint return as a surviving spouse, you only need to file Form 1040X to claim the refund. If you are a court-appointed personal representative or any other person claiming the refund, file Form 1040X and attach Form 1310, Statement of Person Claiming Refund Due a Deceased Taxpayer, and any other information required by its instructions. For more details, see Pub. 559, Survivors, Executors, and Administrators.
