ok so i had rct3 original and i figured out how to import custom scenery. then a couple weeks ago i bought platinum! now i knew that all of my original coasters with custom scenery would be deleted but how do i install custom scnery to the platinum! edition so i can make new ones with the custom scenery

Not too sure what the difference is on the Platinum. I would think that you could place them in the same spot though:
C:\Program Files\Atari\RollerCoaster Tycoon® 3\Style\Themed

no clue srry