Don't suppose anyone knows how to find and delete settings for an extension in VS 2019. I uninstalled one and reinstalled and it was already populated with its previous settings. Its seems surprisingly difficult to pinpoint for some reason.
Just to add to this, I have found out that extensions utilise an options page. Now just to work out where Visual Studio stores all the data entered in an options page.
UPDATE With help from Sergey I have located the settings. They are present in %localappdata%\Microsoft\VisualStudio\"Current version"\privateregistry.bin
To access the keys you need to load the file in regedit(as admin). Then click HKEY_LOCAL_MACHINE and File -> Load Hive and navigate to the bin file and type the name of the Key you want it to load as e.g "VSSettings". Then you can navigate HKEY_LOCAL_MACHINE\"VSSettings" to find settings.
Don't forgot to unload HIVE after as you won't be able to open Visual studio without unloading it first.