run a form for one time in a program

you will need a configuration file. This will contain a flag set to false initially. when the app runs and flag is false, run the form and set the flag to true, so next time the  app runs it wont run the form (because flag is true).

or if your app uses a database you can use existing data layer to set same flag in a database table.

or move this form into its own app (.exe) and call that from the installer.

there are a number of ways each with its own complexity.