In case you want to add an autosplitter file manually (probably because that autosplitter hasn't been approved in Livesplit yet), you need to edit your Livesplit layout, and add "Control --> Scriptable Auto Splitter". Then, go to the layout settings, go to the tab of this component, and set the "Script Path" to point to the .asl file you downloaded.
The ASL file doesn't have to be in the same folder as the game.
Could you stop judging people based on their "view count"?
You are not a true Kirby fan if you never played this game: https://www.speedrun.com/kirbymeme
To add to the above post by @Garsh, if a game doesn’t have a field for additional usernames and you think the leaderboard should support co-op runs, talk with the game moderators about it.