Hello!
Go ahead and verify the game files via the Uplay launcher. This fixes anything that is missing or corrupted.
Here are the steps: Verifying Game Files in Ubisoft Connect for PC - Ubisoft Support.
And make sure you are using the correct trainer for the version of the game you have.
- If you have the game via regular Uplay, this is the trainer you need: Assassin's Creed Odyssey Cheats and Trainer for Uplay
- If you have the game via Uplay+, this is the trainer you need: Assassin's Creed Odyssey (Uplay+) Cheats and Trainer for Uplay