if you are unable to restore missing files and/or the program won’t run after having files removed, i suppose you will have to reinstall the program…
to prevent this from happening again, in the future, you should adjust the avast program’s settings so that it doesn’t automatically delete files that it flags… instead, set it to “ask”…
avast needs to warn people that the “avast” program is set to automatically delete files that it flags, and that it flags lots of legitimate files which shouldn’t be removed…