There are 2 ways to do this, depending on whether you already have a Metrica Sports account or not.
1. I don't have a Metrica Sports account
Go to getplay.metrica-sports.com to open an account.
Add your Key/Code within the form:
After completing the registration your Key/Code will take effect on your account.
2. I already have a Metrica Sports account
Go to cloud.metrica-sports.com and login.
Click on the Settings icon and choose "Add Key" from the dropdown menu:
Add your Key/Code within the form and press Apply:
After this, your Key/Code will take effect on your account.