Here is the step by step process for adding Dynamics 365 Marketing to your dynamics 365 instance.
You can sign up for, install, and use a trial version of Dynamics 365 Marketing for free. Trials last for 30 days.

Few important points to remember :

• You will receive a trial Dynamics 365 instance together with your Marketing trial. You must run the Marketing trial on a trial instance, and can’t install it on a production instance.
• You can’t convert a trial instance into a production instance.
• You can install, at most, one Dynamics 365 Marketing trial per Microsoft 365 tenant.

1. Go to the admin platform of your tenant:  https://admin.powerplatform.microsoft.com/  
   Expand Admin centers and click on Dynamics 365:
   
2. In Dynamics 365 Admin centre, click on Applications tab  –> Select Dynamics 365 Marketing Application  –> Click on Manage:
   
3. Otherwise access this url directly :  https://port.crm8.dynamics.com/G/Applications 
   [Replace crm8 with appropriate region]. Follow…