The plug-in will not be automatically transferred when you install Elements 2019. But, if you still have the installation file for the plug-in, you can re-run it and it will probably install in 2019. If that doesn't work, you can go to Edit>Preferences>Plug-ins and add your Elements 12 plug-in folder as an additional folder:
Or, as an alternative, you can copy the plug-in file to the current plug-in folder.
However, because the old plug-in is probably a 32-bit program, it may not work with the current Elements program.
Finally, you can always keep Elements 12 on your machine, and use it if need be for the Silver efex plug-in.