Moving files to the Virus Chest
http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=501#idt_03

Submitting files from the Virus Chest to avast! Virus Lab
http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=501#idt_07

or send to virus @ avast.com in a password protected zip.file
mail subject: False Positive
Password: infected

It is recomended to use a zip program that also encrypt the file like win.rar or 7zip