Move the file to virus chest: https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=501#idt_03

and submit it: https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=501#idt_07

Alternatively, you can send the file to virus at avast . com In subject put undetected malware and in body, give the link to this topic.