Deceased Parent

My father started his taxes, but filed an extension for 2021 because he was feeling so sick. He passed away. I need to finish his taxes, but I do not know his account log in information because what I see in his files isn't working, so he must have changed it.  Is there a way to get into his account to just finish filing them for 2021 or do I have to start over again?

 

Thanks.