Try Maintenance>Virus Chest>right clicking>restore
If that does not work, is there any way to copy those files again. You might have to delete the contents on the USB drive then replace them.
The three alerts begs the question, wouldn't be safer to keep them in the chest and not transfer the detected files to someone else's machine let alone your own?
Dell Inspiron, Win10x64--HP Envy Win10x64--Both systems Avast Free v17.1.2288, Comodo Firewall v8.2 w/D+, MalwareBytes v3.0, OpenDNS, Super Anti-Spyware, Spyware Blaster, MCShield, Unchecky, Vivaldi Browser and, various browser security tools.
"Look before you leap!" Use online scanners before you click on any link.