Hey DKH-02, welcome to the forums! Sorry you're having trouble launching your game - we'll be happy to help you solve that.
This usually happens when you've activated the game on a different Ubisoft Connect account to the one you're currently logged into. As such, the easiest fix is to have a think if you've had other accounts on other email addresses, and try logging into those on Ubisoft Connect, then try again to launch the game.
If you're having trouble locating such an account, please get in touch by one of our direct support channels, as they'll be able to help you find it. Any of the links below will be great - just remember to include your Ubisoft Connect username and email address, and any other usernames or email addresses you recall having, so we can find your details and get you up and running as quickly as possible.
Facebook PM
Twitter DM
support website
Let me know if you run into any issues following these steps
devtrackers.gg