Evidently, Avast thinks that it is already registered at least in some part of the process. Since I recently registered after updating to 7.0.1451, none of the registration options show for me. Only the Current Status is there showing Registered with 362 days left.
Perhaps in the next few days, your status will change in the AvastUI, and the popup will appear. When it does, the missing buttons may appear. You have a few days to see, but don't allow the registration to expire. The pending Avast program update may also change the status.