You would need to pause the web shield to be able to download it and take no action if the standard shield alerts, it shouldn't on the zip file but would when you try to extract it.
Create a folder called Suspect in the C:\ drive, e.g. C:\Suspect. Now exclude that folder in the Standard Shield, Customize, Advanced, Add
, type (or copy and paste) C:\Suspect\* That will stop the standard shield scanning any file you put in that folder. You should now be able to export any file in the chest to this folder and upload it to VirusTotal without avast alerting.
If you can pause the standard and copy the file to that location, enable the standard shield again.
Check the offending/suspect file at: VirusTotal - Multi engine on-line virus scanner
and report the findings here
the URL in the Address bar of the VT results page. You can't do this with the file securely in the chest, you need to extract it to a temporary (not original) location first.
Send the sample to firstname.lastname@example.org
zipped and password protected with the password in email body, a link to this topic might help and possible false positive in the subject.
Or you can also add the file to the User Files (File, Add) section of the avast chest (if it isn't already in the chest) where it can do no harm and send it from there. A copy of the file/s will remain in the original location, so you will need to take further action and can remove/rename that
Send it from the User Files section of the chest (select the file, right click, email to Alwil Software). It will be uploaded (not actually emailed) to avast when the next avast auto (or manual) update is done.