In Finale there are always multiple ways to do almost everything. In this case an alternative if you prefer hands on and to see everything as it happens you can simply create two new duplicate staves. Use the JW Polyphony plug-in to delete the unwanted notes. You will do this either keeping or deleting the unwanted notes. I prefer this method.
Not better not worse just another way to accomplish your goal.
OK, yes, you do, It is about half way down the page. You can d/l it for free. It is one of my most used JW plugins. If you don't have JW Change you might want to grab it also. I use it all the time too. If you decide to upgrade to Finale 27.3 which I highly recommend you do these two JW plug-ins come as standard equipment and they are updated for 64bit Finale 27.3.
Have you ever installed a plug-in? The hard part is finding your plug-in folder on your computer. Then you simply copy the plug-in to that folder and restart Finale. It will appear in the Plug-in drop down menu.