Hello,
you find the Quarantine in the Interface under Maintenance in the top. Then go to virus chest.
Right click on the files and click on extract fron Chest (third in the list) and save them to the desktop.
Now go to settings in top right and go to global exclusions and add them there, now go back to the chest and right click
on the files and click restore, to restore them to their old place.
You can report them as a false positive here: http://www.avast.com/contact-form.php