Hello! If you purchased Odyssey through Steam, you need to ensure your Frontier and Steam accounts are linked - https://customersupport.frontier.co.uk/hc/en-us/articles/4404175514514-How-to-link-your-Frontier-Account-to-the-platform-on-which-you-play-Elite-Dangerous-
Once that's done, you should just need to use the STEAM LOG IN option on the launcher to access it. To do this, open up the launcher and select Options, then Log Out, then STEAM LOG IN. (You may need to restart the launcher if the button isn't immediately available)
This ensures that the launcher reads your Steam purchases (the standard LOG IN button reads purchase...
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