Your watch must be connected to your Wi-Fi network and your paired smartphone.
On the watch, press and hold Down (the music shortcut key).
Select Deezer.
Optional: If you already have a music provider selected, press and hold Menu then select Music Providers.
The watch will display the message, Open Garmin Connect on Phone.
Select Next.
Your smartphone will ask you to sign in.

Acknowledge the message on the phone which will take you to a Deezer sign in. Depending on whether you have an account, the login process will be as follows:
Existing Deezer users: Enter your login details and select login. From here, skip to Step 3.
New to Deezer: Select Register here, and follow the steps to create your account.
If prompted, enter credit card details to complete the process.
From here proceed to Step 3 to set up some music to sync to your watch.