Media capture on an iPad or iPhone can make use of either the front or rear camera. To change this, open up the workflow in the experience editor. Select a step in the media capture module, anyone will work. On the setting panel, go to "Page Settings"
In Page settings scroll down to Input/Output Settings. Here you can choose if you'll capture with the front or rear camera. Front means on the screen side, rear means opposite the screen.
Save your experience and Sync your app to see the changes.