Licence Key in .dat file?

Just received my key in license.dat file, but nothing on my Mac (or Windows laptop) will open it. How do I free my key and restart my Avast software. The free period has expired and I feel a bit exposed!

Thanks

Open Avast for Mac then in the menu bar choose Avast and select Licence. A window will open for you to browse to the location of your Licence.dat file

fantastic. many thanks.