There isn't a R42 interior created for openBVE yet as far as I know, so you have to code it in yourself, or wait for a developer to create a R42 with an interior.
If you wish to code it in yourself, use the tutorials on BVEStation or look at "The B3D Object"/"The CSV Object" (whichever one you're working on)
in the official website of openBVE.
If you wish to let someone do it, then that's fine, but do not clutter the forum by repeatedly asking developers to make it for you.