You shouldn't need to remove the outside unit. On the inside overhead, remove the covers/filters. You should see a screw in each corner that holds the trim unit up to the ceiling. When you remove those and take the trim unit down, you'll see how/where the baffle fits. It's very obvious how it fits once you get the inside trim down. While you're in there, check the A/C mounting bolts. There's a long one in each corner that should be just snug. Don't overtighten them as it could compress/damage the gasket.
retired USCG aviator
2020 Jayco Greyhawk 29MV/2021 MINI Cooper toad