If the device has already been set up, you can follow these steps to join the device to AzureAD.

1. Open Settings, and then select Accounts.
2. Select Access work or school, and then select Connect.
   
3. On the Set up a work or school account screen, select Join this device to Azure Active Directory.
   
4. On the Let's get you signed in screen, type your email address (for example, alain@Company portal .com), and then select Next.
   
5. On the Enter password screen, type your password, and then select Sign in.
   
6. On your mobile device, approve your device so it can access your account.
   
7. On the Make sure this is your organization screen, review the information to make sure it's right, and then select Join.
   
8. On the You're all set screen, click Done.