Repeating Mail Calendar Reminders?
Edit:  If you're connecting an Exchange account or to a Google calendar via the Exchange setting, the Second Alert option is not available, because these systems do not support a second alert.

If you are not connecting via the Exchange setting you can access the Second Alert like this:


On your iPhone, start Calendar.  
Navigate to the day that has your event.  
Select the event, which brings up the Event Details.
Click the Edit button.
Scroll down until you see Alert.
If the event does not already have an alert, it will say "none" and you click "none" to add an alert. 
Once the event has an alert, you will see a new entry just below it called Second Alert.  It will say "none" and just like the first alert, you can click on it to add another alert.