First, I’m an Avast user and not an Avast Team member.
What were you doing that required a password ?
Have you previously set a password to prevent changes to your Avast Settings ?
I don’t remember making a password for this or I probably did I just can’t remember it.
It’s possible to reset or remove the password but painful.
Clean Reinstall
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- Download the avast! Uninstall Utility, avastclear.exe Avast Removal Tool | Download Avast Clear | Avast and save it to your HDD. Make a note of the steps required or print the page.
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- Download the latest Avast off-line installation file for your Avast Program https://files.avast.com/iavs9x/avast_free_antivirus_setup_offline.exe if you are using this and save to your HDD.
After the clean reinstall there will be no password set for the User Interface and you will have default settings.
All done Thanks brother 
You’re welcome.