With the home version, about the only thing you can do, is wait for the first detection, check the box don't show this again, and click no action. At the end of the scan you will get a list of anything found and you can then deal with it. Further configuration options are availible in the pro version.
But so you don't have to sit by the computer while it scans, you can do this.
Make a note of where avast starts the scan, then place a harmless file, such as one of the eicar test files, near that location. Next time you do a scan, avast will find the file and alert you. Then you can do the steps above.
