Avast Support: Submitting Malware Samples
https://www.avast.com/faq.php?article=AVKB258#artTitle

Submitting False Positive
https://www.avast.com/false-positive-file-form.php

Submitting files from the Virus Chest to Avast Virus Lab
https://www.avast.com/faq.php?article=AVKB21#idt_07

Report a URL
https://www.avast.com/report-a-url.php