how to reinstall dr 18.1

From what I've read here, I need to completely uninstall the current version of Davinci Resolve before installing the older 18.1 version. Is that correct?

And how it is true, any one here who knows how I can backup all my DR settings (DB backup is already done).

I'm not sure about minor updates, but it certainly doesn't hurt to do a full uninstall/reinstall.

This video walks you through how to backup all of your Resolve settings:
Creative Video Tips: Do THIS and Never Lose Any Work - Clean Install DaVinci Resolve 18

My process is to export database/projects and export keyboard shortcuts.
Then I backup these folders and put back what I need after reinstalling (I re-download my Reactor plugins again instead of copying them back from the folder).
%APPDATA%\Blackmagic Design
%PROGRAMDATA%\Blackmagic Design

Thank you very much. That looks very helpful.