To migrate an Exchange on-premise user in a Synchronized or Federated Environment to a Hybrid user:
- On the Active Roles Web interface Navigation bar, click Directory Management.
- On the Views tab in the Browse pane, click Active Directory.
- Click the domain in which you need to create a new user.
- In the list of objects displayed, click the required Container or the Organizational Unit.
- Select an existing user with Exchange on premise and click Azure Properties.
- In the Azure Properties wizard, select the Licenses wizard.
- Select Exchange Online Plan from the License subscription list and click Finish.
An Exchange online mailbox for the user is created.
The Exchange Online created is available only after migration.
Refer the Microsoft link to perform migration from Exchange on premise to Exchange Online mailbox.