I think you missed the target Speedy:
@ vegenesh
If you have deleted a device in my.avast.com, that corresponding device will have to be connected again.
That can't be done remotely, you have to be at that device, open the avastUI, Summary section and it should be saying it is disconnected or not connected, there should be a connect link to the right of that. This should allow you to logon and connect the device to your avast account.