How do I set the event for free development?

To set Sundays (day 7) event, go to the Clash of Zones event screen and select the Overview tab on the top. On this screen there is an 'i' button on the right but towards the top that may be sparkling if you haven't yet chosen an event. It will be on the par that says Today's Event.

Tap this to see a summary of the weeks events so far and on the Day 7 entry will be a button to choose your event. This has to be done though before the Sunday reset (before day 7 starts). If the button is not there it's too late.

Once you have chosen you can go back and change your mind as long as the event hasn't started yet.