Each county in every USA state typically has its own Probate Court, and typically that court has an application to initiate a Probate Court proceeding.
But each court can call this application or form something slightly different.
Simply call the Probate Court in your local county and ask the Clerk for the form to initiate a probate proceeding. The clerk should be able to provide the form to you, or point you to a website where you can download it.