I am unable to complete iOS software update due to password issue. How can I remedy it so I can use the 2021 version TurboTax software?

You could also see if you can reset your password: https://support.apple.com/en-us/HT202860

Hi,

Is there another Admin user account that someone knows the password to so you can use it to upgrade?

Incidentally, I will add that your Mac runs a Mac OS operating system. iPads and iPhones run the iOS operating system. They are two completely different things.