For official reference, see: Avast Support: Uninstall Avast using avastclear
Open Avast > Settings > General > Troubleshooting > Uncheck "Enable Self-Defense." avast uninstall command line
msiexec /x PRODUCT-GUID /quiet /norestart For official reference, see: Avast Support: Uninstall Avast
Use the official avastclear.exe with command-line arguments. For official reference