The only way that can be done really is by confirming false positive (see below) and sending a sample.
What malware name is being given on the detection ?
You could also 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.
Send the sample to
virus@avast.com 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.