It is not so clear to me what exactly you mean with "block" the program.
Do you mean Windows Defender?
Do you mean that the "blocked" attribute is set (properties of the file)?
Do you mean the firewall?
Do you mean Avast blocking from download or running? If this last one is the one, then Avast is doing its job. Change Avast to "ask" instead of "automatically block".
If you already have the file in your system, scan it. If everything is OK, select the file properties and unblock it. Run it again, and in case Avast asks again, select the choice you want.