Hi, Not sure if this has been covered, but adding legacy symbols to the symbol library was a little bit confusing - to me anyway. I have quite an extensive library of custom symbols and hoped to use them in the new much improved version.
It seems that the way to do it (on Windows, not sure if this applies to other platforms) is to enter the symbol editor, Preferences tab, and click on Manage Symbol Libraries.
Select Global and at the bottom of the child screen, click on the folder picture. This will open the search tab. Find your kk library folder (such as my_libs.lib) and add to the list shown. This will be the bottom entry in the list. Click on the Migrate Libraries tab. This will create a new version in the original folder, now called my_libs.kicad_sym. Remove the recently added legacy folder from the list and add the newly created my_libs.kicad_sym in its place. Job done. Your library will now appear in the Libraries page of the Symbol Editor program or in the Eschema Add Symbol function. Big sigh of relief at this end.