If you want to remove an Avast account, you can easily do that in the Settings page of your account.
I’ll show you below how I managed to close my profile using a desktop computer:
1 Go to https://id.avast.com
and log in by entering your email address and password on their website.
2 Click on your username in the right top corner > Profile details
3 In profile details, you’ll see now a Delete account button
4 Confirm that you want to have your account removed
You’ll be logged out automatically and your account has been closed.
*Source (& thanks to): avast.com