Dynamics 365 - Change Unified interface to Legacy interface

This entry assumes that you have or at least you created a trial for Dynamics 365 CRM and signed in.
You can create a trial here: https://port.crm.dynamics.com/G/TrialInstances/TrialInstancePicker.aspx

1. Navigate to https://admin.powerplatform.microsoft.com
2. Click Environments
3. Select the environment you want to change and click the 3 dots
4. In the context menu click Settings
5. Click Products / Behavior
6. Disable "Use Unified Interface only"
7. Click Save