Hello. Welcome to Just Answer.
The splice of 3 existing whites will get your new white wire added to it. The splice of two blacks will get your new black wire added to it. That will get a constant hot and a neutral into the new switch box. In that box, connect the black to the top screw on the new switch, and splice the outgoing white to the incoming white. Connect the outgoing black to the bottom terminal on the switch.
This sounds logical. I need to turn to power back off and follow these directions. I have bookmarked the page so I can return to it after I make the connection.
OK, sounds good. I'll be here for a little while yet.
It works like a champ. You did well. Thanks.
You are most welcome. I'm glad to hear you were successful.