When first loading content discovery, you’ll be greeted with a campaign selection screen, as shown below:

From within this screen, simply select the desired campaign from the drop-down list and click ‘Next’.  However, if you only have one campaign connected to your user account, this screen will be bypassed as you only have one campaign to choose from.

If you wish to navigate back or choose a different campaign, select the ‘Choose Campaign’ from the timeline navigation in the blue bar at the top of the screen.