Click the link above on your iPhone. It will take you to the Playbook app.
Navigate to your favorite Partner.
Tap on the Start 7-Day Free Trial button.
You should now see a Subscribe screen with a Start 30-Day Free Trial button.
Select that button and enter your Apple ID credentials.
Not sure about Playbook?
If you decide Playbook isn't for you, I've provided instructions on how to cancel so you're not charged at the end of the 30 days. See this guide. You can cancel anytime and still maintain access within the 30 day period.
Please don't hesitate to reach out if you have any questions.