You say a virus was found, in most cases it isn't a virus at all but some other form of malware.
- What is the infected file name, the malware name given by avast where was it found e.g. (malware name, C:\windows\system32\infected-file-name.xxx) ?
####
Trojans generally can't be repaired, because the entire content of the file is malware, so it is either move to chest or delete, move to the chest being the best option (first do no harm). When a file is in the chest it can't do any harm and you can investigate the infected warning.
Only true virus infection can be repaired, e.g. when a virus infects a file it adds a small part to it, provided that virus is one which avast has a repair routine for, then it may be possible to repair the file to its uninfected state.
However, for the most part so called viruses, trojans (adware/spyware/malware, etc.) can't be repaired because the complete content of the file is malicious.
