Maybe I have been fortunate, but I used the ADD/Remove in the Control Panel. Then I did a search for all files and folders that contained the word Avast. When that search was completed I deleted all, and that took care of things.
Surely someone with the knowledge to do so will soon help you.
If not then I would consider reinstalling Avast and then going through the process I have found to work in uninstalling and searching and removing.
If you have done that and still have a problem then it will take an Avast expert fo help you.
Best,
Jerry