Redeem via Epic Games Launcher
Open the Epic Games Launcher
Log in to your Epic Games account
Click your username in the upper-right corner
Select Redeem Code
Enter your game key and click Redeem
You should see a success message
Click Back to Home to return to the launcher homepage
Go to your Library, Star Atlas should be there, ready to install
Redeem via Epic Games Store Website
Open your browser and go to https://www.epicgames.com/store
Log in to your Epic Games account
Hover over your profile name in the top-right corner
Click Redeem Code
Enter your game key and click Redeem
Once confirmed, open the Epic Games Launcher
Your game will now appear in your Library