Do you have the suspect file in avast's chest?
If so, then right click on the specific line and scan it. Avast will use the latest definitions. Once avast gives the result as clean, you can restore your file and be confident with the result.
If the result is not clean, then wait for the next update and try again.
You can also resend the file from the chest itself, also with right click. Just leave it there (as oppose to deleting it from the chest), so the file will be uploaded to avast in the next definitions update, if not earlier.