Activate Avast Antivirus:
1. First, open your Avast antivirus software interface that you have installed.
2. Click on Menu on the top right.
3. Go to My Subscription.
4. On the My subscription screen, click Enter a valid activation code
5. Enter the activation code in the text box and click Enter.
6. Check your subscription information for the activation code. Then, click Continue to return to the My Subscription screen.
Finally, your Avast subscription is now activated. The expiration date of your subscription appears in Subscriptions on this PC.