You're referring to a trainer or a cheat code for Assassin's Creed Odyssey, specifically version 1.5.6.
Based on common trainer versions for v1.5.6, these are the most helpful features provided: Resource & Money Multipliers
Download & Launch: Download the trainer from a reputable source. Launch the trainer before starting the game, or once you are in the main menu.
Match the Version: Ensure your game is actually updated to v1.5.6. You can check this in the main menu of the game.
While there isn't a single official "156 trainer" for Assassin's Creed Odyssey
Open Cheat Engine, click the computer icon, and select the ACOdyssey.exe process.
– Provides max Wood, Iron, Leather, Obsidian, and Gems for upgrades. Ctrl + Numpad 3 Infinite XP – Instant leveling to the cap. Ctrl + Numpad 4 Infinite Ability Points – Unlocks all skill tree nodes. Game World & Utilities Invisibility – Stealth through forts without being detected. Ctrl + Numpad 5 No Wanted Level