Once you subscribe to "Automation" subscription plan of SMS Magic, you can go ahead and install "SMS On Workflow add-on" from SMS Magic Portal. To do the same log-in to Customer Portal with your SF credentials and follow the below steps:
- Click on "Get Started" tab
- Click on “Install”
- Then, select “Click here to Install Workflow"
- Then click on “Install for all Users” and then click on Install.
Once the installation is done, you can go ahead and setup workflow rule to send Auto SMS.
You can refer below link for more detail steps on how to setup workflow rule to automate text-: