Put your chart and song in the game, then, replace the costumes of the “opponent” sprite with the opponent of your song. The order of the poses for the opponent are: left, right, up, down, then replace the costumes of the “player” sprite with your oc/you, the poses for the player sprites are right, left, up, down. Finally, replace the backdrop!
Go to SpideyMcPlays chart converter to find more info on converting your charts and stuff.