Hi PLANETSEAN, welcome to the forum
I presume you have been sent the license file, xxxxxx.avastlic ?
This file is to be opened by avast:
Left click avast! tray icon --> Click 'Maintenance' on the left --> Click on the subheading 'Registration' --> Click on the bar that says 'Upgrade' -->Click on the 'Insert avast! Pro Antivirus/Internet Security License File' --> In the window that opens, find and select the license file.
You should then be good to go
-Scott-