Uninstall question

My father in law recently lost his wife, and has started to use her laptop. Avast has been installed under her account and any attempt to uninstall the app requests a PIN he doesn’t know. Only way to reset the PIN is to reset it to her email account - another password he doesnt have.

Using Avastclear.exe also gets to the stage asking for a PIN.

How can I uninstall Avast?

Using Avastclear.exe also gets to the stage asking for a PIN.
Did you run it from safe mode?

https://support.avast.com/en-ww/article/Uninstall-Antivirus-Utility/

and if you still have a problem with the password, try deleting the “aswResp.dat” file
https://support.avast.com/en-ww/article/Remove-Antivirus-password/