If you still have access to your old device, go to Online > Community > View Restore Code .

If you want an endless supply of Gems, you don't need a cheat code. You need a strategy. Experienced players use a method called or "Rerolling."

: A restore code (or transfer code) is a private key used to move your progress to a new device or recover a lost account.

To protect your progress and ensure you can always recover your account: Get LOT'S of Free Gems || Neo Monsters

If you're looking to maximize your gem earnings legitimately:

Occasionally, developers release time-limited gift codes (distinct from restore codes) via official social media or patch notes for small rewards. How to Safely Use and Manage Your Restore Code