I assume you tried deleting the relevant folder in Appdata user folder such as C:\Users\xxxxx\AppData\Roaming\Microsoft ? (Win 10 and ? win7)
One thing I've started to do when troubleshooting is to find out which files I modified recently. Usually I discover I modified something and forgot that I did it! To find out, I run a search in Windows Explorer, from the root of the install. I run searches on *.xml, and *.xdp. Then I sort the search results in date order and just investigate the files which have been modified in the last day or so. Changing the view setting from search to details when looking at the results helps.
I still have CFS3 on my only Windows-based PC, which is old and still running Windows XP. I cannot find an AppData user folder.
And yes, I have updated my stone tools to steel.
Perhaps there is a corresponding folder or file with XP that I can delete?
Yes there is a similar folder whose name I have forgotten but should be Users/XXX or some link like that. It will be under a "Microsoft" subfolder and will have ConfigOverrides, uisel, ViewUI, etc files. Perhaps do a search for those under Users.
Again, what install are you using? Just basic CFS3?
You can remove the whole folder and when you restart the install it probably will ask you to set your cfg again. Do that and also deal with the DPR there under 'Parameter editor for Overrides" by going File > custom settings>window>overrides in the cfg.exe app.