I am very sorry for your loss. 

You, as executor, can get your father's refund, by including Form 1310 - Statement of Person Claiming  Refund Due a Deceased Taxpayer when you file your father's return,

To do this, please follow these steps:

1. While in your father's return, click the Search button at the top right of the screen (magnifying glass).
2. Type form 1310
3. Click the Jump to form 1310 link.
4. On the first screen, mark the Yes button and enter the date of death.
5. On the next screen, Does [father's name] have a certified personal representative?  mark the first button, 

   Yes. I am the court-appointed or certified personal representative [father's name], and click Continue.

6. Continue through the screens entering the requested information.

Please see this TurboTax support FAQ for more information:  Can I file Form 1310 in TurboTax?  

All income received prior to death should be included on his final return.  You should check your state filing requirements to see if you should file that return as well.

My father died in 2020 before his 2019 return was completed.  Can I complete the return as normal or must I do something different?  One of the questions in the step-by-step asked if the taxpayer is deceased,

Yes.

You can complete the tax return for him.  But be sure you have contacted the Social Security administration per the instructions in the link below before filing his return.

Assistance with filing a return for someone who has passed away

Answer yes on the question asking if the taxpayer is deceased and any subsequent questions.

I am very sorry for your loss.