Whilst I don’t use the Avast Secure Browser - if you haven’t exported your settings, bookmarks, settings, etc. prior to uninstalling and reinstalling I believe they aren’t saved anywhere.
This is the information links that you can check, but I believe the above is correct.
- Avast Secure Browser FAQ - See https://support.avast.com/en-ww/article/Secure-Browser-FAQ/.
- Uninstall Avast Secure Browser - Secure Browser Removal tool, https://download.avastbrowser.com/avast_secure_browser_uninstall.exe
- How to Backup your Avast Secure Browser settings: https://support.avast.com/en-eu/article/backup-antivirus-settings/#pc - Make a note of where you save the settings so you can restore them.