Cannot find where to put the activation code even though I have the code

I paid for Premium Security yesterday, downloaded it and have found the activation code but where it then tells me where to insert the code doesn’t seem to be there, and the ‘final’ screen says that my machine is now ‘protected’. But is it? I keep getting alarms from Avast saying that they have removed one (the same one each time) particular virus and and that ‘the threat is secured’ (this has happened about 30 times since yesterday for the same ‘virus’), yet I keep getting pop-ups from other companies saying that I have 7 viruses on my machine! Is my machine safe or not? When I go to the subscription page it says that I haven’t attached Avast to any machine so I should download it! I have downloaded it numerous times (about 20), have copied the activation code but still can’t find where to put it. I’m going round in circles here!

Open UI software > click on menu top right > enter activation code at top. If it is not there do below.

Open UI > click my subscriptions > does it show a date of expiry and also a link to enter code.