iOS: For iOS runners, there is, unfortunately, no way to download the game on iOS unless you had downloaded the game with your Apple account before it was removed from the App Store. If you did download it before the removal, you can re-download it by going to the App Store, pressing the button in the top right to open the Account menu, going to the Purchased section, and then using the search function to search "Yo-kai Watch Land". Then you can proceed to redownload the game.

Android: For Android, you can download the APK for the game via QooApp. https://apps.qoo-app.com/en/app/3934 It's a pretty straightforward process, just need to download the game.

Emulation: I understand that there's likely a good amount of iOS users who can't re-download the game. So, the YWL leaderboard also allows the use of emulators for running the game. The process of downloading YWL for emulators is the same as downloading it for Android.