@Tish,
Most files can’t be repaired.
If you right click on the files in the chest, one of your options is to report that file to
Avast as a false positive.
Doing so will let the guys in the Virus Lab check the file and, if determined to be a false positive,
remove it from the detection. You’ll then be able to select “Restore”.
Files in the chest can’t harm your computer so there isn’t any reason to hurry up and remove them from there.
If after submitting them to the virus lab and then having waited a reasonable amount of time, recheck their status.
If they are still being detected as a virus, then you can always remove them at that time. 