I would suggest always to back up your browser bookmarks to a html file.
In ASB, go to Bookmarks Manager and from the hamburger icon, select Export Bookmarks.
You can then import them again from that file if you need to do a clean install of ASB.
Also do not confuse the Avast Antivirus product uninstaller "avastclear.exe"
with the ASB uninstaller "avast_secure_browser_uninstall.exe"